From the Image::Size documentation:

imgsize(stream)
Returns a three-item list of the X and Y dimensions (width and height, in that order) and image type of stream. Errors are noted by undefined (undef) values for the first two elements, and an error string in the third. The third element can be (and usually is) ignored, but is useful when sizing data whose type is unknown.

So, you're going to want to look in the third element returned to see what went wrong.

In reply to Re: determining image size by a URL by jhourcle
in thread determining image size by a URL by Anonymous Monk

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