Not sure about the GRAPHIC keyword but there’s an article (19313) by Glenn Rose at iSeriesNetwork.com that deals with adding colour to iSeries prints and, amongst other things, image files that are stored in the IFS. V5R3 of the OS must be installed.
There might be a technical possibility that some kind of image could be stored in a GRAPHIC or VARGRAPHIC column, but I’d never trust it. Review SQL Data types. The GRAPHIC/VARGRAPHIC types are generally character strings where the characters themselves are graphics.
Look at using one of the Binary types such as a BLOB.