Here is another way to use CGI - i assume that all images will be stored in a doc_root directory named 'images', and only .png images files are used:

use strict;
use CGI qw(:standard);

my $image;

print header, start_html, start_form,
  textfield('image'), submit, end_form, hr, p;

if ($image = param('image')) {
  $image .= '.png' unless $image =~ /\.png$/;
  print img { src => "/images/$image"};
}

print p, hr, end_html;
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jeffa