Though I am far from a regex expert, I had a thought that I hadn't seen suggested yet: watching you use the first regex to extract $prefix, and then a second to extract $format from $prefix, you could actually combine the two extractions into the same regex: with nested parentheses, the arguments are assigned in the left-to-right order of the open-parenthesis (see perlretut#Extracting matches). Using this, plus stevieb's and kcott's excellent suggestions, my regex snippet would be:

use warnings;
use strict;
...
my ($prefix, $format, $count, $ext) = ($match =~ /(\w+)(%(\d+)d)\.(\w+
+)/) or die "cannot find match";   # EX: Img%04d.png
printf("  \$prefix: >%s<\n", $prefix);      # (\w+)     => Img
printf("  \$format: >%s<\n", $format);      # (%...d)   => %04d
printf("   \$count: >%s<\n", $count);       # (\d+)     => 04
printf("     \$ext: >%s<\n\n", $ext);       # (\w+)     => png
...
[download]