AFAIK, there are no easy way to extract an image from a pdf. On evince, it is quite obvious, you put the mouse over the image, right-click and you get a "save image as...". There is a snapshot functionality in Okular but it is very hard to have pixel precision with this tool.
Created attachment 127096 [details] pdf containing an image
*** This bug has been marked as a duplicate of bug 406489 ***