"美術" is what is called "fine arts", while "芸術" is art in general. In other words, the former is a part of the latter. /The definition of "美術" is, however, not that limited. "美術" usually means not only "絵画" but also "彫刻", "版画", etc. It could sometimes include many other visual artistic expressions such as "書", "建築", "工芸", "写真", and so on. /On the contrary, you usually more often say "芸術作品" rather than "美術作品" even if it is categorized in "美術". In that case, "芸術作品" would sound more like a native speaker of Japanese.