I think your camera must have to have a VFW driver ( video for windows ), or V4L ( video for linux ).I "think" a WDM driver for Windows works too.
Whenever I want to grab photos / single frames from a webcam, I've been opening a video feed. So I can view the live video on screen, and grab an image from that.
Here's full source code to do that :
http://forum.java.sun.com/thread.jspa?threadID=570463&tstart=50
However, since it's opening a video feed, you only get the max video resolution available to JMF.
So if your camera supports still photos at 1600 x 1200, but only video capture at 640 x 480.... then JMF will probably only be able to capture video & photos at 640 x 480.
regards,
Owen