I run a site that has a lot of writers that generate quite a few articles a day.

I require them to provide two image sizes (one for the big headline image and one as the thumbnail). I've been wanting to change up the site layout a bit, but I am becoming limited by the image sizes for the posts.

I have considered just cropping images, but they still need to look nice, and cropping doesn't always generate what I'd want. I'd prefer to just scale down by percentage (as I do with thumbnails).

Should I just make the writers provide more images? How do other sites handle this?