Most of the Ideas area can be branded - it would help to be able to brand the "Thanks for submitting your idea" confirmation in submit-only portals to be a graphic other than the Aha! cartoon of a man holding a sign. You can add your own logo, but not remove the cartoon.
This is currently possible using custom CSS. Customize your portal CSS from Settings -> Account -> Configure idea portals. Select your portal, then go to the Portal branding tab -> Custom CSS.
Use the following CSS and insert the URL of the image you would like to use:
.future-fred-thanks {
background-image: url("insert your image URL here");
background-size: cover;
height: 300px;
}
.future-fred-thanks img { display: none }
Click here for more details on customizing your portal.
Requested via support ticket - making visible in portal.