You could try a file-recovery tool [1], assuming you actually saved it to disk.

If it was in the clipboard, I'm not sure how you'd retrieve it, if you overwrote it with something else.

[1] http://www.bing.com/search?q=file+recovery+tool+windows&pc=Z004&form=ZGAFDF

See:

• Fix problems that cause images to not show

• A way to see which images are blocked is to click the favicon (How do I tell if my connection to a website is secure?) on the left end of the location bar.
• A click on the "More Information" button will open the Security tab of the "Page Info" window (also accessible via "Tools > Page Info").
• Go to the Media tab of the "Tools > Page Info" window.

• Select the first image link and scroll down though the list with the Down arrow key.
• If an image in the list is grayed and there is a check-mark in the box "Block Images from..." then remove that mark to unblock the images from that domain.