NASA is a major source of such pictures, but observatories and space-related institutions around the world contribute too. You need special viewing software to look at these pictures. Nowhere is there a more dramatic and important use of global networking than among the medical community. Physicians and medical students can now look at diagnostic images from patients all over the world. Many of those sites are open to the public, with confidential identifying data removed, of course.
Some sites are searchable by medical condition and other specific criteria.
Some sites are general, covering several disciplines like gastroenterology, oncology, gynecology, and so on. Be sure to examine all the links to see if your topic is covered. Just because the first page is general does not mean that's all there is. A few diagnostic imaging sites cover veterinary medicine. Sometimes news sources feature scientific pictures.