A photo has to be a picture created through a photographic process. This means that very often Ink-Jet prints are not allowed as part of a visa application if detected. Many consulates do the "scratch-test" to see if it is genuine. This is because the Ink-jet print is not file-safe as the genuine photo.

The photo must be of the same kind that you would use for your passport, which means that it is recent, frontal, width about 35-40mm, and preferably on a white background. There is a guide to a good photo here. (.pdf)