Most competitions that I have seen need an actual print to judge, as opposed to the digital image (which is a file). Most competitions also require that entered artwork be original (and not say, a limited edition reproduction).
With my own work I print monoprints, so that is my original. I also print reproductions of the monoprint, but obviously I am not entering them into competitions... since they are basically glorified posters, in a way.
Even if the work is original, some competitions (like say, the Duck Stamp competiton, http://duckstamps.fws.gov/~9143746.pdf
) specifically BAN all digital works and digital prints!
See here for more info on that issue. A final verdict to ban digital prints has already been reached... it's disheartening. Someone complained that a digital print won. From what I saw of the debate, they were claiming that they had no way to know it was an original print... they said they had no way to know if copyright had been violated. But, of course, that's just as true for any other media as for digital work! Using reference photos without permission, for example.
So my suggestion is that even if the competition says "all media" or "no prints", that you call and specifically ask, and make sure you'll be able to enter. Getting disqualified is a waste of everyone's time and money!