Well, you could offer your images on every product and let the buyer chose.  I think your quality would suffer though.
 
Not every image is going to look great on every product. And, in my opinion, part of what is being bought is your taste in editing to what is best.

And if the image isn't the right size for the product's template it's going to look really awful.
Trust me on this one, I bought samples of my planned inventory before I opened my store. When I say awful, I mean really really awful. Blurry, jagged, just horrible.