First, I gotta say, the "how do you do X without WELL-KNOWN-WAY-TO-DO-X?" questions bug me. It means you've got an artificial constraint, but you aren't being explicit about the constraint, so I can't tell how close to the optimal way you can get.

In particular, I can't tell why you can't use Image::Size, so I don't know which of the problems below to solve:

• You already have something called Image::Size that does something different (so rename this one)
• You're not allowed to install modules in the normal @INC path (so put this one in your own lib)
• You don't know how to install a module (read perlmodinstall)
• You want your program to self contained (take the source of the module and put it in a BEGIN block in your program)
• There's something broken with the current module (fix it, tell the author)
• This is a homework assignment (disclose that!)
• Other things I haven't thought of

So, we spend time solving the problems we hallucinate instead of the actual problem.

Half the battle of a problem is discovering the universe of solutions before narrowing it down to a working solution. Saying "I want X without Y happening" is a very fuzzy goal indeed.

-- Randal L. Schwartz, Perl hacker