how to transfer image from camera to PC via USB

Hi.

I want to transfer image from camera (which outputs parallel 8-bit signal) via usb to computer. I guess standard arduino COM is to slow,and also full image transfer via atmel is to much.
Is there an usb shield that i could use for it?

So basically I just want an "web cam" attached to arduino. I would also like just one usb line from arduino to pc.

thx

So basically I just want an "web cam" attached to arduino.

Have you tried doing a search for people asking this question?
You will find the arduino is not suited to video applications, not enough processing power or memory.