Sir William, yep they're purchasable as posters on the cafepress page, in 16x20" size. I made your photo work, but that was only about 0.75 megapixels. Most cameras these days are between 4 and 12 megapixels.
It's possible that photobucket resized it down. (as an aside, any pictures you upload into the knight pages do get resized, but the original is stored for any future resizing, so we can use that as a mechanism to get them here).
Oh yeah, I encourage everyone to take lots of good pictures in interesting places.
When it comes to editing them into alternate backgrounds, it works best to have relatively neutral lighting (no camera flash, really heavy shadows, or overexposed blasted-out whites) and no obstructions or anything else that needs to be edited out before pasting the person into a backdrop (such as shadows on you from other objects).
For instance, if you have a photo with part of you that is obscured by another person or object, then that portion of you still has to be hidden in a new scene (see Sir Ulrich's, I had to keep him in the lower-right corner of the photo, because that's all there was to work with). Or if you have a patchwork of shadows over you from tree leaves, then any new background that's pasted in will also have to be a tree-covered scene with similar lighting.
Some people who are masters at photo-editing can completely remove shadows or change the angle of them. I might be able to tweak them a bit, but I'm no master at it. In the first post in this thread, I took out a shadow in the foreground in the grass by using the "levels" control, but doing that sort of thing on complex objects, such as faces, is an art form.
Since I'm still a novice at this, I'm still a bit limited by the source photos.