Humanline's images are available to educators and students for free re-use provided that the attribution guidelines are followed. There are two licensing agreements that users need to be aware of when attributing the works they're re-using. Those licenses are rights-managed and royalty-free. You do need to register as an education user to access all of the images for free.

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Why not control robots with your arms? Fire lasers from your head? Steal piles of candy? Fiddle with toilet seats hands-free?

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"To enhance access to its rich and varied collections, the Harvard College Library has digitized thousands of historical photographs, pamphlets, manuscripts, books, music scores, rare maps and other rare and unique materials. The vast majority of these images are freely available online for public access"