add the frame in the same way as you did it with your Mosel-pic ;-)
I have heard some rumors about plug-ins for frames but I think using such a plug-in would be against the honour of serious digital editing.... At the end the frame has got a minor importancd...
Usually I would build a frame as shown at your example with different coloured layers and sizings.
f.e. for a pic of 900x600 pixel
- sizing of the pic to 862x562 pixel (final size minus total frame size x 2)
- conversion of the background layer to a "normal" layer.
- (canvas) resizing of the pic to 868x568 pixel
- adding a layer behind the picture layer and fill it with black
- (canvas) resizing of the pic to 870x570 pixel
- adding a layer behind the other 2 layers and fill it with red.
- rezing of the pic to 900x600 pixel
- adding a layer behind the other 3 layers and fill it with black.
- merge all layers to one background layer.
Much easier but yith correct borders would be a workflow with selections
-> sizing of the pic to f.e. 900x600
-> selecting the areas to be coloured with the marquee tool and fill it with colour....
After all: For me frames are less important, but still the "tray to serve the pic". By I have generated a couple of templates to variate and copy them to pics.......