This is just an enhancement request. What do you think about allowing a way to shrink an image and then extend the background to meet the thumbnail dimension requirements?
For example, my default thumbnail size is 150x150. I have an image that is 300x450, but all of the image is important for the thumbnail. What I want to do is proportionally shrink the image, making it 100x150, and then add 25x100 of background color of my choice filled in on both sides to make it 150x150.
This plugin is already great, but if this were implemented, I would like it even more. =}