To include an image in a Campaign, you'll need to use an Image URL, which will input the photo right into the Campaign!
As long as the photo exists somewhere on the internet, just right-click on the photo and select "Copy Image Address", which will create this Image URL.
You can then click on the photo icon in the Campaign message edit toolbar and paste the URL.
To see the message from the student view, you can use Preview Message.
This will display a pop-up example of exactly how the message will look to the students: