A possible solution:

#!/usr/bin/perl -w

use strict;

# Here go all the top-level categories
my @categories = qw(clocks daisies);

# And the subcategories.
my @subcats = qw(vert red);

# Directory contents.  You could also loop through STDIN or
# something. See the comment below the foreach loop.
my @names = qw(clocks001.jpg clocks002.jpg
               clocksvert001.jpg clocksvert002.jpg
               clocksvertred001.jpg daisies001.jpg);

foreach my $name (@names) {
# while (my $name = <STDIN>) {
#     chomp($name)
    # Get image number and strip off the extension
    my $output = "$name -> ";
    my ($im_no) = $1 if $name =~ s/(\d+)\..+$//g;

    foreach my $cat (@categories) {
        if ($name =~ s/^$cat//) {
            $output .= "category: $cat; ";
            next;
        }
    }
    $output .= "subcats:";
    foreach my $subcat (@subcats) {
        if (not $name) {
            $output .= " null/null";
            last;
        }
        if ($name =~ s/^$subcat//) {
            $output .= " $subcat/1";
        }
    }
    $output .= " IM#: $im_no";
    print "$output\n";
}
[download]

Arjen

Update: Fixed a small bug in the output.