if you wanted to renaming inside the folders for say imagesr like akjs.jpg bigpacks.jpg etc and rename them to 1.jpg 2.jpg 3.jpg.
Code:
#!/bin/bash
i=1;
shopt -s nullglob;
for f in *.{jpg,jpeg,JPG,JPEG,gif,GIF,png,PNG}; do
ext="${f##*.}";
ext=${ext,,};
ext=${ext/jpeg/jpg};
mv -- "$f" "newfolder/$i.${ext}";
((i++));
done