What you need to do is use metadata. So, setup some keywords based on what is in the picture. these can be anything that is relevant to you and the pictures you take. You could start with something like: People, Animal, Scene, Still Life, Abstract, etc. You can always add more keywords as you go, so for your animal pictures you could add bird, insect, mammal, fish, etc. to better differentiate different pictures. Keywords are just one type of metadata, you can also add place data based on where the photo was taken (this is really useful, espcially if you have a gps logger to tag this). Search around for more on metadata and exif which is the specific data for pictures.
All the best
Andrew Wright.