How do I embed a call to action button (with a link to a form)
on an image? I can do it if I use the Marketo templates, but need to do it in one of my own templates to adhere to CI?
You're going to need to build a container and specify the image to be the background image, then you can layer elements on top of the background image, such as a CTA button. Some simple HTML/CSS should do it. Here's a pretty straight forward w3schools example: How To Create a Hero Image
Another option is to save the image you want and use an image editing tool like photoshop or Google Drawing to add what appears to be a button with text on top of the image. Export the new image that has your background and what looks like the button that you added to it, add that to you email and hyperlink the entire graphic. Downside is that the button will not be responsive separate from the image and the entire graphic is then hyperlinked. Just another option for those that want to avoid digging into the code.