[Red Dragon Audio]

It wouldnt work as well as plain fabric, but you could always put fiberglass behind a real canvas painting. I've heard it works decently. Watercolor would work better than oils or acrylic but hard to find on canvas.

Beat that's a great idea----You could always comission someone to do a watercolor painting on linen; linen would be more acoustically transparent than canvas.  Use that black 1" -2" thick insulation board from Knauf as the backer behind the painting so it doesn't reflect any light through the porous linen cloth.

(I just use Knauf as an example all the time b/c I am familiar with their website and products...no affiliation).