Ok, Step 2:

After sumbitting the message with the attached file, you will edit it to put the image:

- click the link of the attached file on your message, the image will open (on a different window)
- Right click on the image
- "Copy image url"
- Go back to your message
- Click Edit
- Place the cursor where you want the image
- click at the "Enter image" icon
- Click any of the options (non floating, left, right,..)
- At the text box, right click, "paste"

There you go