Images from national laboratories, relevant to energy. Each lab has its own site. Different labs have different conditions on use, but most of the images are public domain or under Creative Commons licenses.
"Many such images, all located in the “public domain,” are included here, and they are copiously indexed. For the most part, the images have been scanned from volumes to be found in the University of Washington Libraries. The more than 21,000 images were taken from a variety of publications issued between 1735 and 1924."