I use https://tinypng.com/ to compress my website's image files. I save them out of photoshop at 75% quality then run them through tiny png and it makes the images nice and small without loosing any noticeable detail.
I think my image got butchered by the forum image compressor in the last contest too I made it the size of a standard magazine spread for the purpose of my portfolio but when it got shrunk down to forum image size you lost all the quality in my line and subtle texture. I was bummed. I don't want a portfolio full of postage stamp-sized illustrations just cuz thats what jumps out the most when you're flipping through the slideshow.