@alltypes = qw(.gif .jpg .jpeg .jpe .jfif);
for (1..5) {  # No need for a c-style loop.
    if param("im$_") {
       ($filename = $ext = $file = param("im$_")) =~ s/.*[\/\\]//;  # Simultaneous copy/substitute.
       $ext =~ s/^[^.]*(\.[\w]+$)/$1/; # There are better ways to check for a file, like grepping to make sure the file *ends* in the right extension, and getting rid of $ext, IMHO, unless you're using the extension somewhere...?
       unless (grep {$ext eq $_} @alltypes) {
       error("Your image needs to be a GIF of JPEG file!");
       }      
    } 
}