I’m just now starting to get to a place with my own poster work that I’d like to post some of it online and the question has arisen, post a photo of the print or digital design? Well thankfully I’m not the first to ponder this question and I’ve dug up a lively debate on the topic over on gigposters.com from a couple years back. I’m still on the fence, mostly because my photos look pretty disappointing but Dan MacAdam from Crosshair posted some great info on shooting your work that I’m anxious to try out:

Stick it to a flat board or panel with tape loops or spray tack.
Take it outside…indirect sunlight or overcast is best…make sure the sun isn’t reflecting off it or hitting it at a weird angle that lights it unevenly.
If you have a DSLR… Set ISO low, 100-200 if light allows. White balance to whatever is appropriate. Use a tripod, or of none is available make sure your shutter speed is 1/250 or faster.
Do not get right up close…that will give you distortion and vignetting. It’s better to stand several feet back and zoom to fill the frame.
I’ve been using a 50mm f/1.4 prime lens recently and it has worked really well; ultra sharp and good color.

If you shoot RAW you can tweak the white balance after the fact…it seems like that’s the hardest thing to get right.
I haven’t tried shooting with a custom WB because I’m too lazy.

Checkout the full conversation on the gigposters.com forum.