Once your picture has been uploaded, find its image location address (URL) by right clicking on the image and copying the image location. The URL will look something like:

http://somepicturesite.com/yourpicture.jpg.

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=... (This code looks different than the code below, because it will actually produce a picture link instead of just a picture.)

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">
_____________________________________

If your picture is too large to fit nicely into the text page, you can add a width attribute.

The command with the width attribute would look something like:
<img src="http://somepicturesite.com/yourpicture.jpg" width=600>
_____________________________________

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 (but with the correct image web address).