If you use an iPad or iPhone, you can look up apps for journals/personal diaries that allow pictures to be attached. Each of my my rats have a page with a good pic attached to it. Easy to keep up with age, litter birth dates, litter size, which male was used to breed, etc. It makes it easier to see who is doing what and when. Especially if you have a VERY large colony. At some point, they all look the same. Lots of browns... Lots of hooded with spots... LOL