You can participate in the following seven categories:
People in Science
Scientists in their natural habitat.
Optical, electron, and scanning probe microscopy images all fall under this category.
Audio and video files, computer-generated imagery, etc.
Thematically linked images, that can be viewed as one set. Image set could be made up from up to 10 separate images. In the last case image names must be similar to each other (named in a progressive pattern like “Name 1.jpg”, “Name 2.jpg” etc).
Wildlife & nature
Organisms who grow or live wild in an area. Macro photography also falls under this category.
That collects all images related to astronomy. May it be the images of stars, people viewing them or the equipment used for it.
Everything else goes into this category, from archaeology to vulcanology.