There are plenty of ways to save pictures you find on Flickr. One way of doing so (in Firefox) is right-clicking the browser page and heading to View Page Info -> Media. This is too much work.
Flickr layers a transparent file named spaceball.gif – a 43 byte 1×1 px file – over some images, rendering the traditional right-click -> save as…, or dragging the image to the address bar methods useless. This simple technique probably fools most people, but you can simply bypass this by right clicking the bottom edge (1-2 pixels in height) of an image and saving as usual. You can also drag the image from the last row of pixels and drop it where ever you like.