Use SHIFT + F10 to bring up the menu you'd normally see when right-clicking.

Use the "context menu" button on your keyboard (if you have this key, it looks like a small arrow clicking on a menu) to bring up the menu you'd normally see when right-clicking.

Grab images even if right-click is disabled

View the source code for the Web page, figure out the direct URL for the image, enter that URL into your Web browser.