I was deeply involved in the project for 5 years and the reason you can't download from it is because museum partners don't want you to. All the image security you find there comes from partner requests.
If it's irritating, don't blame Google.
The word "security" can't be applied when the measures in place are "don't include a download link".
There is no "security" when the image displays perfectly fine on the screen. It just takes a few screens worth of panning, screen-grabbing and assembling a complete image in Photoshop. After a few rounds, I had a rather efficient workflow going using macros. Most of the artwork I was interested in was between 50 and 100 years old, and completely for personal use - printing out hi-res versions on paper of my choice (matte, never glossy like almost all commercial art prints.)
No. Don't shift the blame to other parties. Google decided to play ball with all these external requests. Google owns the project. Google is the one to blame.
Sorry, also no. Let me be clear, museum partners would not sign contracts - and thus the project would not exist - if these stipulations about preventing downloading were not met. It was a dealbreaker across the board, and Google's compromise was a good one. Without it there would not be this access to art and culture.
