Picasa also has an option (down on the right side) you can click to "Link to this photo". But it's not as easy to use.
This trick will work with any of the hosting sites:Step 1: Upload your photos to your photo account (PhotoBucket, Picasa, etc.)
Step 2: When you're ready to post the picture...
Internet Explorer: From your photo account (Photobucket, Picasa, etc.) "Right Click" on the photo you want to post, and click "Properties". Highlight the Address (URL), and "Copy" it.
FireFox: From your photo account (Photobucket, Picasa, etc.) "Right Click" on the photo you want to post, and click "Copy Image Location".
Step 3: Go back to your forum post, click the "Insert Image" button and "paste" the URL inside the IMG tags.
It will look something like this ► [img]HTTP://Photo_URL_Goes_Here.jpg[/img]
When you click "preview" or "post" your image will show up.