I recently started a second Etsy shop for non-edible paper items (so that people won't buy real paper thinking that they can put it on a cake and eat it, which wouldn't be good.) I was working on some digital download clip art of some of the brooches that I have, which are the same ones that I use to make molds.
I decided to try applying some wafer paper brooch images to the back of the molds they correspond to to see if plain isomalt plus the pictures would work to make a decent-looking edible brooch. It did work, with some shapes being better than others.
I printed out the brooch images, cut them out, then applied them to the back of the molds after filling them with clear isomalt. The picture showed through the isomalt, and the shape of the molded sugar gave the pictures some dimension. These would work well for a treasure chest cake or a jewelry box cake. Depending on the shape of the brooch, they could also work for a wedding cake, but that would have to be a mold that was easy to pour without overfilling it.
Here's a video showing how I did these brooches. The molds and corresponding images are available on my website here: Mold set to make edible brooches