hi there, generally would use "U" channel or flat bar strips to fit snuggly around bottom and sides of frame. depending on the frame the sides may need to go right to top and onto top of frame to lock it in. Bottom bar either has countersunk holes to screw structure into surface, or attachments below for securing into some structure. Depending on importance of frame it may be possible to screw through support into frame in a discrete location on frame for added security. Have also be done this using side of support, rather than bottom, to have frame projecting out from wall to allow both side to be seen.