I have seen this before and usually it is down to the web browser Print Settings. Most browsers by default will not print background images (Imagine if you visited a website with a black background and tried to print as you saw it on your screen? Your black ink cartridge would probably be gone in a few days!).
If you are using IE (Internet Explorer), go to a webpage, then click on Tools, Internet Options and select the Advanced Tab.
Go through the list until you see a heading for Print and put a tick in the box beside the option that says 'Print background images'. Select OK to close the windows and then try to print. You should see all images on your printed page.