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Doing it online imposes a 1mb file limit. Most pictures I've taken are 2.5-5mb. I know I can always knock down image quality, but with the downloaded version I can run any quality picture through it.

Don't forget it's going to be made into a halftone anyway – you'd be as well upping the contrast and making it greyscale anyway, and even if making it greyscale doesn't make the file smaller, I'm sure you could do that manually and it wouldn't affect the quality of the rasturbation, as it's essentially a lo-res halftone anyway.
 
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