Voyager's EMH is apparently simply a collection of photons and force fields, controlled by a computer, either on board Voyager or in his mobile emitter. Yet he seems to see and hear things from the perspective of where his holographic eyes and ears are, even to the point of reading printed text (as in the Season 5 episode "Warhead" where a sentient missile has taken over the Doctor's holomatrix and reads information off a screen). How does this work?
The EMH like other holograms possesses a hardened form that allows it to hold devices and touch surfaces. This hardening implies the hologram has a complex matrix that can emulate physical things like visual and aural sensors. The hardening need not be permanent. There are scenes where things sometimes pass through the holograms.
Season 3 Episode 24 of Voyager "Displaced" actually delves into this a fair bit.
After the crew is abducted without any tricorders or other equipment they escape by adjusting The Doctor's "optical sensors" via the mobile emitter to allow him to see thermal energy and find the microwave signature of a portal through a field around their prison.
The scene comes complete with a short first person shot which appears to indicate his optical sensors generate an image imitating that of human vision.