Yup, pictures on bitcoin L1 is a bad idea for many reasons.
From the artist point of view, it's not possible to put an original art file, such as a high quality PNG file of 6k x 6k pixels, on bitcoin L1. There's no space for that. As a result, anyone can falsely put a low resolution version of other artists art on bitcoin L1. An artwork being placed on bitcoin L1 therefore does not prove copyright, authorship or ownership.
The best approach is to host art on bitcoin L2 via multiple hosting services. If one goes down you have backups. The artist can submit some high quality proof-of-work with watermarks on L2 and signal his/her authorship of the art to the market. This would de-monetize stolen art.