Hi Paul,
XNView is good for changing images from various file types to another. Also handy for resizing, clipping, etc and it can categorise your pictures.
XnSoft
Mutate and Survive
On two occasions I have been asked, — "Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?" ... I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question. - Charles Babbage