If you want to save webcam images to your device external memory (usually SD card), there are two possibilities.
From webcam preview menu, choose "Save to gallery" or "Save time.lapse".
First option saves the image to Gallery (the same location where you save photos taken with your camera), and the second one saves the images to a subfolder under /sdcard/.recordings.
From version 4.0 favorite images are not cached on SD card anymore, but the the latest image is downloaded. This is the reason why you cannot find images on SD card cache anymore.