Flickr's good, sure. What I like to do is this.
1. Go to the photo's page on Flickr.
2. Go to ALL SIZES and pick the size you want to show up in the thread - medium is usually good.
3. Right-click the image and hit "Copy Image Location." (This varies from browser to browser; I'm using Firefox, and you should, too. )
4. Go to your post and enter:
(Paste the image location instead of "URL.")HTML Code:[img]URL[/img]
5. If you want, go to the largest image available on Flickr, and copy the URL in the address bar of your browser.
7. Then modify the part of your post so it looks like this:
URL2 is the pasted address, URL is the same as before, and the lowercase url should just be typed in exactly like that.HTML Code:[url=URL2][img]URL[/img][/url]
If you're having trouble, though, it's easier to just use ImageShack or PhotoBucket. They give you the code really easily.