Only licensed attorneys are authorized to provide legal advice, which involves applying legal principles to a specific person's set of facts. We are not licensed attonreys so please consult with a licensed legal professional for legal advice. Below is our non-legal response to the OP.
In general, there is no law against inaccessibile images. If there were, most of the internet would be in volation. Some states (e.g,. California) have explicit requirements that the websites of state agencies be compliant with ADA (i.e., WCAG) however, that has been poorly enforced. If you are asking about the upcoming DOJ regulations, then it appears the legal onus is on the campus that adopts the remix and perhaps the instructor although that is unclear to us at this time (and probably unlikely). The original author of the inaccessibile content nor the harvester that brought it into the LibreTexts (if not automatic integration) do not appear to be responsible.
However, if there are Intellectual Property violations (not using openly licensed content or nor attributing the content properly), then the author and harvester are targets for legal action. The Digital Millennium Copyright Act (DMCA) provides some protection for LibreTexts as the platform in these cases depending on several factors.
