Flaps
Depends on whether or not the image was 'placed' on the webpage. If it's one that was, you can place the pointer over the image (using the trackpad), click and hold (using your thumb, and then drag the image to your desktop (using your finger). Then release your thumb and bobs your uncle.
Editing requires an image manipulation application (i.e. Adobe Photoshop).
Trips
Edited to add: AM, we need to get a life!