Nice job, for your one of your earliest Perl scripts!
I especially commend you for using GD.pm as I have been learning it in detail lately, and enjoy seeing other code utilizing this great module.
The only changes/modifications I would make if you felt like doing them, would have to just be:
Converting the Spanish text to English, (for easier readability for English-speaking persons. Or perhaps, the english equivilents maybe?) :)
Creating a more-detailed error message (at the end of the script - which is: else { print "Error :( "; } to let the user know what really went wrong, or what the user needs to do different.
Use -w otherwise known as warnings simply so you can check to make sure that everything is in good shape - I did check to make sure that it was fine, and it was in this scripts' case, but make sure to add this in future scripts. :)
Otherwise, great job on your script! Keep up the great work, shadox!