One of the easiest ways to provide your photo to be embedded into a post is to upload it 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. There are also picture galleries here on Gardenweb that could be used, but they have more limited functionality.

Once your picture has been uploaded, find its web address by right clicking on the image and copying the image location. Some sites may even provide the address in a text box below the photo for your convenience.

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, type this command into your post (substitute your picture's address):

img src="http://somepicturesite.com/yourpicture.jpg">;

Note that I had to use special characters to get the command above to show up here without turning into a picture, but you can use it as shown (with the correct image location, of course).