dyeing linen

[caiusbeerquitius]

So, one can discern evidence of dress from art. In fact, the paintings of ships of the Dutch artist William Van del Velde are so intensely accurate that they were used for intelligence purposes at the time.

Yes, some "modern" art is basically photorealistic. Ancient art is quite different, though. But for the picture you provided: Are the folds and fabric-widths "accurate"? (I don´t know, that´s why I ask)
But still you couldn´t necessarily tell whether it is from wool or linen or silk, what kinds of weaves were used, what kind of dye etc. Similarly you couldn´t tell from a Roman relief whether the helmet depicted on it was made from brass, bronze or lead or even tin, if you had no access to finds.