One extremely bothersome fact about this forum is that when you upload a picture, it is automatically resized to about 500x300. This is the only way we can run this site free of charge with unlimited uploads.
However, there are at least two ways to counter this:
If you're requesting high-res images from someone, don't be shy, go ahead and ask, either on the forum directly or by personal message to the specific member. Be prepared to provide your email to them, so they can send the pictures to you.
Please note that images are no longer resized to that horrible resolution (thank goodness!), and are actually pretty decent quality now. However, most super high-quality images uploaded here are still not the original quality, therefore the above suggestions still stand.