You can put as many pictures as you want to in a post. Just use html instead of GardenWeb's built-in picture thing.

Upload your photo(s) onto an image hosting site such as Photobucket, Flickr, etc. That should be pretty straight forward, and the individual sites will give instructions on how to get your photos uploaded to their site when you sign up.

Once your picture has been uploaded, find the image's location address (URL) by right clicking on the image and copying the image location. Some sites may even provide the appropriate HTML code in a text box below the photo for your convenience. It will be the one that begins with a href=...

Let's say, as an example, that the address of the picture you want to post is http://somepicturesite.com/yourpicture.jpg

To embed the picture into a post, use the command:
img src="http://somepicturesite.com/yourpicture.jpg">;
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If your picture is too large to fit nicely into the text page, you can add a width attribute. This is a good idea to keep posts from being hard to read.

The command with the width attribute would look something like:
img src="http://somepicturesite.com/yourpicture.jpg"; width=600>
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Note that I had to use special characters to get the commands above to show up here without turning into pictures, but you can use them as shown (with the correct image web address, of course).