You can do this in two ways,

1) Install the Firefox extension offered by vi.sualize.us which lets you easily bookmark pictures from any website by just right clicking on the image and

2) Copy the image URL and paste it on the "Post" form and it will fetch the thumbnail for you.

vi.sualize.us also lets you share pictures using your personalized URL (e.g  http://vi.sualize.us/syedabbas) , comment and tag these images with your online friends and with other users on vi.sualize.us. One thing to be careful about is that the "Safe" feature on the site does not work all the time, I saw a few pictures which fall under 18+ category with "Safe" feature on.

No copyright issues have hit vi.sualize.us so far however the site clearly states that the content (pictures) on the site belong to their original owners.

You can view my collection of pictures here: http://vi.sualize.us/syedabbas