optic

Although the object is virtual, light entering the camera would form a REAL image on the film, and thus can be recorded.
From the thin lens firmula:
1/u + 1/v = 1/f
i.e. 1/v = 1/f - 1/u
Since for a camera, the lens used is a convex lens, thus f must be +ve.
if u is virtual, i.e. -ve, u = -[u], where [u] is the absolute value of u
we have, 1/v = 1/f + 1/[u]
hence, v must be +ve, the image formed by a virtual object is therefore a real image