Hiyas and welcome, RD.
It's easy if you have an account at Imgur or some other pic-hosting website:
1. Load the pic to your hosted photos account.
2. Open up the photo there.
3. Right-click on the photo, and then left-click on "copy image address" to copy it to your clipboard.
4. In the reply box here, click on "Insert image". It's the icon between the chain-links and the smiley, above the text-box.
5. Select "by link" at the top of the box.
6. Paste the image address into the box.
7. Click on "insert image."
You can also do it by pasting the image address, in your text reply, between a set of [img ] tags.