I pulled a face the instant I caught sight of your ^.*(\..*)$ regex: the leading ^.* looks pretty pointless, the trailing (\..*) overly generic. For some background on where I'm coming from see the classic old node from 2000: Death to Dot Star! by Ovid.

Given you say "the image is guaranteed to end with the picture extension" I would write it something like: /\.([^.]+)$/ or /\.([a-zA-Z0-9]+)$/ or /\.(\w+)$/ or some such, depending on your requirements, the point being to be more precise than the dreaded "dot star". To illustrate, using GrandFather's example test program: 

use strict;
use warnings;

my @tests = (
    ".",
    "",
    "A sentence.",
    ".gitignore",
    "word.doc",
    "a.dotted.name",
    );

print /\.([^.]+)$/ ? "Matched '$1' in " : "Failed", " '$_'\n" for @tes
+ts;

[download]
produces: 
Failed '.'
Failed ''
Failed 'A sentence.'
Matched 'gitignore' in  '.gitignore'
Matched 'doc' in  'word.doc'
Matched 'name' in  'a.dotted.name'

[download]

If you give us a lot more specific examples of strings that should match and ones that shouldn't, we can offer a more precise regex.

See also: Rosetta code

Update: For an alternative to regexes, using instead mostly standard Perl facilities, such as glob, opendir, readdir, File::Glob, File::Basename, File::Copy, File::Spec, Path::Tiny and Path::Class::Dir, see:

In reply to Re: My regex works, but I want to make sure it's not blind luck by eyepopslikeamosquito
in thread My regex works, but I want to make sure it's not blind luck by SergioQ

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