how to do image processing by mathlab

i am trying to do image processing by mathlab 7. i can run the demo operation. But when i try to do image processing with a picture from my destop it is showing error" undefined file" .I have change the directory but nothing is happening.

can any one tell me what the problem is and how can solve it/
regards
samina

It would seem mathlab (matlab?) does not recognize the type of file (extension) of your picture. What type of picture files does mathlab recognize?