As mentioned in PLANET-1112:

Please define a setting in the p4-settings with the label "404 background image", which should be selecting an image from the media library.

Also, add a wysiwyg box that overides all 3 lines of the top part of the text (not the search)
There should also be a comment for the editor to put an image min size -> (kelli will see what it is).

label: 404 Page text