Now that we're talking about inserting pictures, there's one more thing to tell you about the Ribbon: Some tabs appear only when you do specific tasks.
For example, when you:

Select a picture that you have inserted into a message…

…you'll see that
Picture Tools appear on the Ribbon.

The
Format tab includes commands that you can use to edit the picture before you send it.
When you click away from the picture, Picture Tools disappear.
You'll see similar behavior if you include a chart, drawing, diagram, or table in your message.