Make backups of your server directories.

Re-read the documentation for the File::Find module.

Remember to use fullpaths, with/or the $File::Find::dir var, examine the chdir no_chdir flags. Do some extensive testing pre-production run, to ensure your routine does what you want it to do / think it does.

my $count = 1;

sub do_this{ 
 ...
 next unless $_ =~ m/(.*)(\.jpg)$/;
# untaint = $1,$2

# rename(OLDFILE, NEWFILE);
 rename($File::Find::dir.$1.'.jpg', $File::Find::dir.$count++.'.jpg');
}
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Also IIRC you will want to next rather than return inside the &do_this routine.