If you have a hotmail account you can use Skydrive (it sometimes does odd things to the colours though but it's free).

Then it's just a matter of pasting the image address into the little tree box field second from the left of the reply text tool bar thing in front of you.

Remember to scale the pictures down so they don't overwhelm the thread you are posting in (if people want to see them full sized they can right click on them).

Flicker isn't a good option as a host as you have to be logged in to see them.