We have all needed to fix, edit or modify an image on the fly at some point or another. Here are a list of some free online photo editors that do just that and more. In addition to letting you do things like resizing, rotating, and optimizing brightness, contrast, and colors, many of these will actually apply filters (blur, sharpen, etc.) and other weird fun effects, such as giving your image an old-fashioned border or making collages. So you can pick the one that fits your needs, from simple image correcting to elaborate artistic creations.
Check them out: