diff --git a/docs/src/Submakefile b/docs/src/Submakefile
index 7611b346612..2787b84f446 100644
--- a/docs/src/Submakefile
+++ b/docs/src/Submakefile
@@ -944,13 +944,17 @@ $(foreach L,$(LANGUAGES),$(eval $(call HTML_COPY_RULE,$(L))))
 # $(DOC_OUT_HTML)/<lang>/<topic>/X.html.  The source images are in
 # $(DOC_SRCDIR)/<topic>/ regardless of language (translations are
 # image-symlinked to English originals via the sed below).
+#
+# src="..." covers displayed images; href="...png" covers click-to-enlarge
+# targets from image:thumb[link=...] (which would otherwise 404).  The
+# extension filter keeps page/anchor hrefs out.
 .html-images-stamp: $(DOC_TARGETS_HTML)
 	set -e; for HTML_FILE in $^; do \
 		HTML_REL=$$(echo $$HTML_FILE | sed 's%^$(DOC_OUT_HTML)/%%'); \
 		LANG=$$(echo $$HTML_REL | cut -d/ -f1); \
 		REST=$$(echo $$HTML_REL | cut -d/ -f2-); \
 		HTML_DIR=$$(dirname $$REST | cut -d/ -f1); \
-		for IMAGE_FILE in $$(grep -oE 'src="[^"]+"' $$HTML_FILE | sed 's/src="//;s/"$$//' | grep -vE '^https?:|^data:|^/'); do \
+		for IMAGE_FILE in $$(grep -oE '(src|href)="[^"]+"' $$HTML_FILE | sed -E 's/^(src|href)="//;s/"$$//' | grep -vE '^https?:|^data:|^/' | grep -iE '\.(png|jpe?g|gif|svg|webp)$$'); do \
 			IMAGE_DIR=$$(dirname $$IMAGE_FILE); \
 			IMAGE_PATH=$(DOC_SRCDIR)/$$HTML_DIR/$$IMAGE_FILE; \
 			mkdir -p $(DOC_OUT_HTML)/$$LANG/$$HTML_DIR/$$IMAGE_DIR; \