Embedded email header image doesn't show when I send the email

[Jane LSS]

Hey there, I've been trying to add an header image to the top of my emails, but I'm struggling. Here's what I do:

1. Attach the file
2. Go to the body of the email and click to insert an image
3. Select that image via the box that pops up
4. Send the email

I've sent it to my personal account to test it out. I get a blank white box where the image should display and the image shows as an attachment at the bottom of the email.

Clearly, I'm missing a vital step - any ideas?