Some images in Flickr are protected so that nobody would save them to their computer. This is done by overlaying the image with a transparent spaceball.gif image. You can see this in action in the following image.
Here when the save Image As option is taken you can save only spaceball.gif which is a simple 1×1 transparent image. So how do you save such images. One method that will come to your mind immediately will be saving it from cache. Yeah that works, but there is a method which is a lot easier. You can use this in Firefox.
When you right click on any page opened in Firefox you can see an option Page Info. (Note that a similar option is viewable under the DOM Inspector) Click on that, Goto the Media tab. This can also be accessed through Tools » Page Info You can see that here there is a list of all Images, Music and Shock wave objects used on the page Just click on the image name you want to save and select Save As. Thats it.
One you get familiar with images in Flickr you can see a similarity in all the main images addresses used in Flickr ages. Just check the image. You can easily spot tis one after some trial. Also any object can be saved fby using this method.
You might also be interested in knowing how to disable right clciks using simple HTML tags. If this method is used you can select Page Info from Tools menu on the top.