zett - 5:30 pm on Apr 3, 2012 (gmt 0)
you need to prove your copyright in advance of going to court as no infringement can occur until a right is proven
How can you prove that YOU are the original copyright holder (even without formal registration)?
For photographs, for example, you as the creator of a photo typically do not put the high-res original files online, but ALWAYS a smaller image. So you can easily prove in court (or, if you want, also in the court filing) that you are the creator. All you have to ask the infringer is - "Please show us the original file, and tell us how you modified the image." Typically, the infringer will just admit that he can't do that. Dumb infringers will make up a story and maybe even provide an upsampled version of the image that they claim to be "the original". Until you show up with your 16 MP RAW file. If the infringer still insists, let an expert take a look at both originals. :-) :-)
Hard rule: Never post high-res originals online!