Knowing American English, no one declares income there. People report it (give information rather than clarify what's already partially-known). Both are correct, I believe, but reporting an income is much, much more common in the U.S.
A declaration from the perspective of how American English is used sounds voluntary rather than factual (I'm dictating reality), and it is more of a clarification as I mentioned (I think this is one of the differences between the two words).
I can declare that I made 50k that year, but it may not be true. I hold all the power over the figures. By reporting my income, I'm telling you as it is in actuality (or at least the "actuality" that I want to believe it to be).
I know in Russia, for example, you declare your residence (because you've got the power to tell a fact rather than to tell a past event that you may not actually have any power over). That's really the same as reporting it (the address, of course), so that the local authorities know where you live.