It has been considered, but rejected for simplicity and reasons.
Although it is possible (see here:
How to Rotate Images Using JavaScript (JavaScript & Canvas). Cross-browser Solution. — ajaxBlender.com), it would complicate the code and won't be much use (you can rotate only in certain steps). Much better solution (from my point of view) is:
a) photograph level pictures
b) Use straighten/level tool that you find in almost any good photo browser/editor. (
Google Picasa,
IrfanView etc.) - thus you will have straightened picture for future use.
once you have picture with level ground, you can freely use it