Oh, wow, those are amazing. Plus, I've always liked Code Lyoko. Really, my only favorite thing about them is how the characters look so serious. Are you planning on making some for Ulrich and Odd? Anyway, keep up the good work.
Code Lyoko, very nice. They're really good, while a bit plain. But no one said plain was a bad thing. And how did you make these exactly? But I gotta say the Ulrich one in Lyoko is probably my favorite. You seemed to have centered that one pretty well.
There were lots of tricks to making these but the main techniques were cropping, color splash, and fill.
All the stocks you used were pretty low quality. That already takes away from the overall look. In addition the majority don't have a focal point. The background's all over the place and doesn't lead the eye anywhere, and with the stock just slapped on over it, it's not entirely visually appealing. The best one you have in terms of flow and heading in the right direction is this one. The cropping's not bad, there's one focal point, and the blue on the side sort of points in the direction you'd want the person to look in. Generally you want to avoid putting things dead center. As for the signature...well, to me it seems to be less of a signature tag and more of an image that's got a sepia filter on it and was cropped. Again, there's no real flow or anything interesting to look at. I'd recommend looking up some tutorials for whatever program you're using as well as looking up some basic art concepts, like the rule of thirds. It'll help you a lot down the road.