Most of the photo editing tools that I have used have a crop feature that allows you to choose the aspect ratio of the crop (e.g., 8x10, 5x7). If you use this, it will guarantee that your resulting image is in the right shape. Use that feature so that you can choose the crop, not the printer's computer.
Sounds like this is the answer to my question about sizing it in Photoshop, right? But, using this method, every time you get a print order you'd have to open PS, do this to the original, save it, then upload that image to the printer? That's not a real problem for me right now, considering the bleakly small amount of printing I've had to do thus far, but what about when I (not IF I!) get busier? I guess when filling a print order, I could just see which images were not acceptable using the original, and resize just those...
. Yeah, looking at it I realized I set the 5x7 from the 8x10 crop instead of the full.
