Several commercial web sites offer the facility for users who have a subscription to develop and store their family history and display it in various ways. These sites have proved to be very popular and usually also offer DNA testing.
While much of the information will have been assembled diligently and carefully by the the tree owners, it is important to be aware that other trees will have been assembled inaccurately and carelessly by people without any genealogical knowledge. Some trees contain large amount of information copied from other people’s trees, apparently done without checking. It will be obvious from this that errors can be multiplied – sometimes many, many times.
So take great care when using this resource. Always check any information you use against an independent source, contact the tree owner for their permission to use it, and ask them where it came from if you find what appears to be an error.
The same sites allow photographs and documents to be uploaded to illustrate trees. Once in place these images can be freely copied by downloading them. The original uploading or subsequent copying (or both) might be in breach of copyright law – it is important to bear this in mind too.
See DNA testing for related information.