I've noticed recently that some of my fanart looks pretty different depending on the computer that you're using.
I use an Apple laptop and my decisions are made from how it looks on that, but the contrast can change wildly on other computers, especially PCs. Not really sure what to do about it, but I have gotten complaints that some images were "too dark". To be honest some of them were, others may look wrong based on your monitors, sorry.
Oh, and hpcompanion.com -check it out.