ah, cropping, my least favorite aspect of photography. it has always been a pain to me on whether to crop or not to crop. I tend to shoot a lot of images at lots of different angles or POV. It's not unusual for me to take 60-70 images of say a statue for instance, from every angle, setting, or concievable way of shooting it. Some of the cropping is as has been said "in camera". however after looking through all of the images, I might find that just a "certain angle" or whatever looks a little better if cropped a bit differently. I guess a lot of it has to do with how I feel about the image after a second or third look. the "mood" that I was going for when I shot the image may change with time so that the crop changes some what after the fact. I think a lot of it has to do with the fact that "technically" I don't have a clue to what I'm doing, I shoot by "eye" or feeling. Basically seat of the pants flying style of photography. I'm afraid that if I were to actually learn how to shoot, I might lose the "creative aspect" of my photography. So it's rather hit or miss, but sometimes I get lucky and get a decent shot. as for mats, I tend to use storebought standard sizes.