To scrape, start here
http://metmuseum.org/api/collection/collectionlisting?offset...
and increase 'offset' by 100. The JSON output contains image URLs. The total number of results is 441048, so finding another endpoint that doesn't enforce a limit of 100 on the 'perPage' argument would be great.
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EDIT: thanks to spitfare, I updated the perPage argument to 100. The site doesn't allow larger values, but that's definitely a great start! (about 4k requests to get everything)