Hey @Ben18! Are you sure that the image you're referring to isn't being added via your email template, rather than via the incentive email editor? If so, it won't be able to be removed. You can view your account's templates here25. (All of your account's incentive emails will use your account's default email template.)
We also have a separate guide on our incentive email editor here24.
If you're still having trouble, I'd recommend reaching out to our team at firstname.lastname@example.org (or via the in-app messenger in your account) with a description of the issue and the name of the form(s) in question. One of our Product Specialists will take a look at your account and help you to troubleshoot more specifically :)