In order to include images in your autoresponders and broadcasts, you'll need to send as "HTML". So make sure you have the HTML tab selected while editing your autoresponder.
Put the cursor roughly where you want the image to be. Click on the media icon in the editor.
IIf the image is already online and you know the image url, you can paste it into the URL box otherwise click on the icon on the right to open up your media library.
Next, click on the "upload" button
Now click the "Choose files" button which will open up your computer files locally where you'll find the image you want to include in the email.
After you've selected your image(s) now click "Upload to server"
Now click the name of the image you just uploaded, which should show you a preview of it, and then click on "Insert"
After you hit the "Insert" button you should see your image appear in the email.