Blowups and no sense of proportion!

I can't get over how few people seem to understand the concept proportion. No drama, and nothing abstract or conceptual here, just the literal ratio of height to width. I get a lot of requests to enlarge a photo or piece of artwork to fit a certain area (usually to fit a standard-sized frame), and the toughest concept for people to GET seems to be this: if I enlarge it one direction, it's going to be enlarged the other direction too. Either that, or it gets stretched or scrunched. I'd think that anyone who works with images would have a good grasp of this idea, but apparently not.

I dunno if anyone will ever see this, but I'm going to make a recipe to follow here.
Divide the desired width by the original one. Take that number and multiply it by the original height. If that result is the same as the desired height, then you've got an original of the same proportion as the new size you want, and you can enlarge it without having to crop it. If not... guess what. Something's getting cropped off.

The options:
1) "float it" -- sort of like the "window box" that movies sometimes use if they are being shown on a TV screen.
2) Distort it -- if it's scanned digitally for enlargement, it CAN be enlarged more one way than another to fit; sometimes you can get away with it if it's not to drastic. Don't try it on a portrait though. Yuck.
3) Get a custom frame made.