Rename all *.png files by their md5sum.png name

$ ls -1
file1.png
file2.png
$ md5sum *.png | perl -pe "s/([^ ]*)  (.+$)/2 1.png/g" |tr " " \n | xargs -n 2 mv
$ ls -1
257ad8424ed04f7a07e4175b1a3d91f3.png
e0ea852f2f2d9564429842f7863af499.png