Pictures of unconstructed subjects which look humanoid or powerfully suggest a recognizable uniquely human characteristic: clouds, rocks, trees-- whatever.
Unconstructed here means that the subject was not deliberately made by someone to have the human feature or image. Examples of appropriate images would be: tree roots that strongly suggest a human hand, a rock which looks like two embracing people, etc....
The real concept of the group is for the pictures to cause the immagination of the viewer to percieve a human characteristic.
Note: There is a similar group, facial impressions which is more restricted to human face shapes only.