Use original image to compare

Author: ledyba-z

.github/workflows/check-image-decoding.yml

@@ -49,7 +49,8 @@ jobs:
             echo "Ignore: ${file}"
             continue
           else
-            score=$(compare -metric PSNR "${file}" "decoded/${file}.png")
+            orig=$(cat Makefile | grep "^${file}" | sed "s/^${file}: \(.*\)$/\1/")
+            score=$(compare -metric PSNR "${orig}" "decoded/${file}.png")
             echo " * ${file}: ${score}"
             if test $(echo "${score} >= 30.0" | bc -l) -eq 0; then
               exit -1