diff --git a/backend/app/services/question_figures.py b/backend/app/services/question_figures.py
index d54950d..18a2e18 100644
--- a/backend/app/services/question_figures.py
+++ b/backend/app/services/question_figures.py
@@ -42,6 +42,28 @@ def figure_json(link: QuestionMedia, asset: MediaAsset) -> dict:
         "caption": link.caption or None,
         "path": getattr(asset, "path", None),
         "position": link.position,
+        # What the library knows, for an explanation figure only.
+        #
+        # Once the answer is in, the catalogue entry is worth having: the
+        # title, the description written when the image was filed, where it
+        # came from, and any marks an educator drew on it. Before the answer
+        # it is a giveaway, which is why the caption fell out of the figure
+        # itself — so it rides only on the rows that are already withheld
+        # until answers are revealed. Nothing here is sent with a stem.
+        "library": _library_json(asset) if link.role == "explanation" else None,
+    }
+
+
+def _library_json(asset: MediaAsset) -> dict | None:
+    if asset is None:
+        return None
+    return {
+        "title": asset.title or None,
+        "caption": asset.caption or None,
+        "alt_text": asset.alt_text or None,
+        "source": asset.source or None,
+        "source_url": asset.source_url or None,
+        "overlay": asset.overlay or None,
     }
 
 
diff --git a/backend/tests/test_question_figures.py b/backend/tests/test_question_figures.py
index a57ef87..2f3bc61 100644
--- a/backend/tests/test_question_figures.py
+++ b/backend/tests/test_question_figures.py
@@ -39,6 +39,24 @@ class FigureCaptionTests(unittest.TestCase):
         self.assertNotIn("title", figure)
         self.assertEqual(figure["path"], "uploads/hip.png")
 
+    def test_the_library_record_rides_only_on_an_explanation_figure(self):
+        """Once the answer is in, the catalogue entry is worth having.
+
+        The server already withholds explanation figures until answers are
+        revealed, so hanging the library record on those rows — and only those
+        — puts it in front of a reader who has finished the question and
+        nowhere near one who has not.
+        """
+        self.asset.source = "Teaching file"
+        self.asset.source_url = "https://example.org/x"
+        stem = QuestionMedia(id=3, question_id=9, media_id=5, role="stem", position=0)
+        back = QuestionMedia(id=4, question_id=9, media_id=5, role="explanation", position=0)
+        self.assertIsNone(figure_json(stem, self.asset)["library"])
+        shelf = figure_json(back, self.asset)["library"]
+        self.assertEqual(shelf["title"], "Right SCFE, AP pelvis")
+        self.assertIn("right hip joint", shelf["caption"])
+        self.assertEqual(shelf["source"], "Teaching file")
+
     def test_what_the_question_itself_says_is_shown(self):
         link = QuestionMedia(id=2, question_id=9, media_id=5, role="stem",
                              label="Figure 1", caption="AP pelvis at presentation.",
diff --git a/frontend/src/components/FigureStrip.css b/frontend/src/components/FigureStrip.css
index e162f08..8cb560d 100644
--- a/frontend/src/components/FigureStrip.css
+++ b/frontend/src/components/FigureStrip.css
@@ -48,6 +48,29 @@
 }
 .fs-overlay img { display: block; max-width: 100%; max-height: 70vh; margin: 0 auto; border-radius: 8px; }
 .fs-overlay-cap { margin: 10px 0 0; font-size: 0.85rem; line-height: 1.6; color: var(--text-muted); }
+
+/* The image and anything drawn on it, in one box: the overlay is positioned
+   against this, so it has to be the size of the picture rather than the
+   panel around it. */
+.fs-overlay-frame { position: relative; display: block; width: fit-content; margin: 0 auto; }
+.fs-overlay-mark {
+  margin-left: auto; padding: 4px 10px; font-size: .78rem; font-weight: 600;
+  border: 1px solid var(--border); border-radius: 999px;
+  background: none; color: var(--text-muted); cursor: pointer;
+}
+.fs-overlay-mark.is-on { border-color: var(--primary); color: var(--primary); }
+
+/* What the library holds, under what the question said. Set apart, because
+   they are two different voices: one was written for this question, the other
+   catalogues the image wherever it turns up. */
+.fs-overlay-shelf {
+  margin-top: 12px; padding-top: 10px; border-top: 1px solid var(--border);
+  font-size: .82rem; line-height: 1.6; color: var(--text-muted);
+}
+.fs-overlay-shelf strong { display: block; color: var(--text); font-size: .88rem; }
+.fs-overlay-shelf p { margin: 4px 0 0; }
+.fs-overlay-source { font-size: .78rem; }
+.fs-overlay-source a { color: var(--primary); }
 .fs-overlay-nav { display: flex; align-items: center; justify-content: center; gap: 16px; margin-top: 12px; font-size: 0.82rem; color: var(--text-muted); }
 .fs-overlay-nav button {
   min-height: 38px; padding: 8px 14px; font: inherit; font-size: 0.82rem;
diff --git a/frontend/src/components/FigureStrip.jsx b/frontend/src/components/FigureStrip.jsx
index 8724004..ea38536 100644
--- a/frontend/src/components/FigureStrip.jsx
+++ b/frontend/src/components/FigureStrip.jsx
@@ -1,5 +1,6 @@
 import { useEffect, useState } from 'react'
 import { uploadUrl } from '../utils/uploads'
+import ImageOverlay from './ImageOverlay'
 import './FigureStrip.css'
 
 /**
@@ -16,6 +17,12 @@ import './FigureStrip.css'
  */
 export default function FigureStrip({ figures, attemptId, size = 'full', label }) {
   const [open, setOpen] = useState(null)
+  //: Whether the educator's marks are drawn. Off until asked for, like every
+  //: other overlay: marks shown before somebody has looked answer the question
+  //: for them.
+  const [marked, setMarked] = useState(false)
+
+  useEffect(() => { setMarked(false) }, [open])
 
   useEffect(() => {
     if (open === null) return undefined
@@ -26,6 +33,13 @@ export default function FigureStrip({ figures, attemptId, size = 'full', label }
 
   if (!figures?.length) return null
   const shown = figures[open]
+  // What the library knows about this image. Sent on explanation figures only,
+  // so it appears after the answer and never beside a stem. The thumbnail is
+  // unaffected either way: in the explanation it shows what the *question*
+  // says about the figure, which is what an educator wrote for this question.
+  const shelf = shown?.library || null
+  const shapes = shelf?.overlay?.shapes
+  const hasShapes = Array.isArray(shapes) && shapes.length > 0
 
   return (
     <>
@@ -59,11 +73,35 @@ export default function FigureStrip({ figures, attemptId, size = 'full', label }
           onClick={e => e.target === e.currentTarget && setOpen(null)}>
           <div className="fs-overlay-inner">
             <div className="fs-overlay-head">
-              <strong>{shown.label}</strong>
+              <strong>{shown.label || shelf?.title}</strong>
+              {hasShapes && (
+                <button type="button" className={`fs-overlay-mark${marked ? ' is-on' : ''}`}
+                  aria-pressed={marked} onClick={() => setMarked(v => !v)}>◫ Overlay</button>
+              )}
               <button type="button" onClick={() => setOpen(null)} aria-label="Close figure">✕</button>
             </div>
-            <img src={uploadUrl(shown.path, attemptId)} alt={shown.caption || shown.label} />
+            <span className="fs-overlay-frame">
+              <img src={uploadUrl(shown.path, attemptId)}
+                alt={shown.caption || shelf?.alt_text || shown.label} />
+              {marked && hasShapes && <ImageOverlay overlay={shelf.overlay} />}
+            </span>
             {shown.caption && <p className="fs-overlay-cap">{shown.caption}</p>}
+            {/* Everything the library holds, once the answer is in: what it was
+                filed as, the description written for it, and where it came
+                from. The thumbnail keeps the question's own words. */}
+            {shelf && (shelf.title || shelf.caption || shelf.source) && (
+              <div className="fs-overlay-shelf">
+                {shelf.title && shelf.title !== shown.label && <strong>{shelf.title}</strong>}
+                {shelf.caption && shelf.caption !== shown.caption && <p>{shelf.caption}</p>}
+                {shelf.source && (
+                  <p className="fs-overlay-source">
+                    Source: {shelf.source_url
+                      ? <a href={shelf.source_url} target="_blank" rel="noopener noreferrer">{shelf.source}</a>
+                      : shelf.source}
+                  </p>
+                )}
+              </div>
+            )}
             {figures.length > 1 && (
               <div className="fs-overlay-nav">
                 <button type="button" disabled={open === 0}
diff --git a/frontend/src/components/FigureStrip.test.jsx b/frontend/src/components/FigureStrip.test.jsx
index 8e8aefb..c1eb90c 100644
--- a/frontend/src/components/FigureStrip.test.jsx
+++ b/frontend/src/components/FigureStrip.test.jsx
@@ -56,3 +56,42 @@ describe('figures on a question', () => {
     expect(screen.queryByRole('button', { name: 'Next ›' })).not.toBeInTheDocument()
   })
 })
+
+it('shows the library record when an explanation figure is opened, never on the thumbnail', async () => {
+  // Two voices. The thumbnail carries what the *question* says about the
+  // figure — words an educator chose for this question — and the opened
+  // viewer adds what the library holds: what it was filed as, the description
+  // written when it was catalogued, and where it came from. The library half
+  // rides only on explanation rows, which the server withholds until answers
+  // are revealed, so none of it can sit beside a stem.
+  render(<FigureStrip attemptId={7} figures={[{
+    id: 1, role: 'explanation', path: 'x.png',
+    label: 'Figure 1', caption: 'AP pelvis after fixation.',
+    library: {
+      title: 'Right SCFE, AP pelvis',
+      caption: 'An X-ray of a child\u2019s pelvis showing the right hip.',
+      source: 'Teaching file', source_url: 'https://example.org/x',
+    },
+  }]} />)
+
+  // Nothing of the library on the thumbnail.
+  expect(screen.queryByText(/Right SCFE/)).toBeNull()
+  expect(screen.queryByText(/Teaching file/)).toBeNull()
+  expect(screen.getByText('AP pelvis after fixation.')).toBeInTheDocument()
+
+  await userEvent.click(screen.getByRole('button', { name: /Open Figure 1/ }))
+  const viewer = screen.getByRole('dialog')
+  expect(within(viewer).getByText('Right SCFE, AP pelvis')).toBeInTheDocument()
+  expect(within(viewer).getByText(/pelvis showing the right hip/)).toBeInTheDocument()
+  expect(within(viewer).getByRole('link', { name: 'Teaching file' }))
+    .toHaveAttribute('href', 'https://example.org/x')
+})
+
+it('carries nothing from the library on a stem figure', () => {
+  // The server sends `library` only for explanation rows; if that ever
+  // changed, the stem must still show only the question's own words.
+  render(<FigureStrip attemptId={7} figures={[{
+    id: 2, role: 'stem', path: 'y.png', label: null, caption: null, library: null,
+  }]} />)
+  expect(screen.queryByRole('button', { name: /Overlay/ })).toBeNull()
+})