Sounds like a bug in ImageMagick or (not very) possibly IIS. You'll probably have more luck asking on the ImageMagick mailing list. The problem is extremly unlikely to be the greater-than test, most likely it's the Ping method that goes into a tailspin.

I wanted to comment on the following piece of code though:

$imgparams{THREED}=5;
if ($image_x>$gallerycfg{'3DWIDTH'}){$imgparams{THREED}=1;
            }else{$imgparams{THREED}=0;}
    unless ($imgparams{THREED}<2){
        &writelog ("Error blah blah $Absolute_URL.",1);
        &dieerr("The image blah blah inconvenience.");
    }
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Which, really, is very ugly. For one, that longwinded if can be expressed with a lot more brevity: $imgparams{THREED} = $image_x > $gallerycfg{'3DWIDTH'} ? 1 : 0; See perlop for the ternary operator. Much more important though, is your error trapping practice. Perl has mechanisms to recognize an undefined variables as such, even to distinguish between a hash entry with and undefined value and one that doesn't even exist in the hash. In this case something like the following would be a lot more appropriate:

unless (exists $imgparams{THREED}){
    &writelog ("Error blah blah $Absolute_URL.",1);
    &dieerr("The image blah blah inconvenience.");
}
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Then again, this makes no sense at all in your case, since the previous assignment will always either 0 or 1 to the key, so your error check is never going to trigger. I think what you were really trying to do here was something like this:

my ($image_x, $image_y);
unless(($image_x,$image_y) = $image->Ping($Absolute_URL)) {
    &writelog ("Error blah blah $Absolute_URL.",1);
    &dieerr("The image blah blah inconvenience.");
}
[download]

Makeshifts last the longest.