If you are looking at an image online, within your web broswer, you can usually save the image to your computer.
For Firefox:


For Internet Explorer:
Note: If you do not see a menu appear, or you see a warning message, when you right-click on an image then the webmaster may have disabled the right-clicking and saving of their images in this way.
Note: Unless otherwise stated it should be assumed that all images are copywrited by their creators (and are their creative and intellectual property) and are therefore not to be used without explicit consent.