A picture frame's rebate ( or rabbet in the USA ) does not cover or hide from view a great deal of the art being framed. Typically, it is  be around 5 to 7 mm, depending on the moulding ( picture frame ) manufacturer. The circle in the accompanying illustration shows a typical rebate width and ensuing artwork coverage. This "covering" of the artwork normally occurs with all picture frames an photo frames and there are no simple or inexpensive ways to avoid it.  Of course, one could use  a clip frame,  which not being a "proper" frame, has no intrusive rebate and therefore can display the entire artwork  but clip frames are a very different product ...