Lower quality images if using Imageshack?

I'm in the content creation stage of building my forum. I'm posting recipes and menus from restaurants, and the images from imageshack take a hit when viewed on my forum.

I checked my image size limits, but it doesn't seem to have any bearing on the images I've posted. I tried every size imageshack gives you, from large to very small. They all seem to suffer a quality loss, except for maybe avatar size (and who would see that level of detail anyway)

Is this a problem with imageshack? Or...