You can attach photos and other files to your message template, but you can embed a photo directly in the body of the message as well.
First, you will need to convert the image into a link. There are several websites that offer this service for free, such as postimages.org.
1. Choose a file to upload
2. Resize image if desired
3. Select an expiration date (not recommended)
Once the file has been converted, look for the "Hotlink for website" link. Copy and paste this into the body of the message template. It should look something like this:
<a href='https://postimg.cc/image/sfxdiva53/' target='_blank'><img src='https://s15.postimg.cc/5r86jasrf/exterior07.jpg' border='0' alt='exterior07'/></a>