Hi,
If you want a popup image with the email input. Create a image the size that you want the popup, set the popup to the same size and add the image to the popup.
You will need to set the image to the background so you can see the email input field and the call to action button.
Select the image you have for your popup then click the 3rd button on the toolbar “Move Backwards” clicking this button will put the image behind the input field and call to action button.
Hope that helps.
Let me know if you have any further problem I can always do a screencast for you to show you how.
