Wikimedia Commons has no built-in image editor currently. It should have a built-in image editor that allows images to be rotated, cropped, etc.
This is related to bug 7757.
Version: unspecified
Severity: enhancement
See Also:
T18877: Moving a page over a redirect should remove entries from the RC table
T9757: allow cropping images when rendered
If Bug 28700 would be fixed, one could at least use a canvas for image manipulation (unfortunately there is only PNG export in some browsers, but one could "grab the pixels" and then JPEG encode, which in turn would be very slow but could work as a background worker) and offering something much more powerful for SVG editing (Bug 38271) without having to install anything on the server except (static) files. (There are solutions around that work 100% at the client side after the application and the file was loaded.) One could also attempt to manipulate JPEG (and the attached metadata) using JavaScript directly. All this requires modern browsers and huge JS libraries. I guess you don't want to process everything at the server...