JdeBPI want to screenshot a user-space VT being realized on the framebuffer.
There are three framebuffer dump programs that I know of: fbdump, fbgrab, and fbshot. None of them work on #FreeBSD, because its framebuffer device works in a different way.
So writing a program to dump the frame buffer it is, then.
It looks like PBM files are the easiest output format.