Making a blog banner

Is a lot harder than I thought it would be. I wanted to create one of those artsy ones. But after spending a large amount of time trying to load a long skinny picture like I've seen on other blogs I gave up. No matter how many times I re-sized the picture in PSE (photoshop elements) I couldn't get it to work. The picture would look fine in PSE but then blogspot would shrink/adjust(?) it so that it would be a lot smaller than what I was uploading. So I'm taking a break for now and I'll try it again at a later date when I am fresh and have more time to spend on it.