A picture frame rabbet ( or rebate ) does not cover or hide from view a great deal of the art being framed. Typically it would  be around 3 to 5mm, depending on the moulding (picture frame) manufacturer. The red strip in the accompanying illustration shows a typical rebate (rabbet) width and ensuing artwork coverage. If none of the artwork may be covered and absolutely everything, image and margins, must be visible, then rather than a picture frame, perhaps a clip frame would suit better than a picture frame. If the incidental coverage of the artwork is something a customer wants minimized then a skilled ...