Use imagescroll feature.

regress/image-sixel-region-scroll.sh

@@ -0,0 +1,21 @@
+#!/bin/sh
+
+# The PR's SIXEL imagescroll check, with known cell pixels and no shell race.
+# Check the default repaint and an overwrite merged with trusted scroll damage.
+
+PATH=/bin:/usr/bin
+TERM=screen
+export TERM
+[ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
+
+python3 -B - "$TEST_TMUX" <<'PY'
+import sys
+from image_scroll import check_scroll, check_capability
+
+for command in ('linefeed', 'up', 'down', 'reverse'):
+    check_scroll(sys.argv[1], True, command=command)
+    check_scroll(sys.argv[1], False, command=command)
+check_scroll(sys.argv[1], True, mixed=True)
+check_capability(sys.argv[1], True)
+check_capability(sys.argv[1], False)
+PY