Antique picture in wooden frame

picture is approx. 5 x 7.  it is metallic gold on glass.  the picture is on the back side of the glass in metal.  glass has imperfections in it.  frame is pine or fir held together with tiny nails. painted with black laquer on sides and brown laquer on front. Had a back tacked on at one time that is gone.  string added to hang it was post manufacture and tied of an original nail and a tack not original.  has a signature that i cant make out.   looks like "F. diaz T scribble". don't know who the portrait is of.  May be thomas jefferson or a family porttrait.  purchased at yard sale.  only info was that it was in a an uncle's house when he passed away.