This is a very common Japanese tradition that people send greeting cards to everyone they know on new year. This is the way to thank others and try to keep their relationship longer. Some people do not contact at all but they still send greeting cards to update what is going on in that family or person. usually they put pictures of themselves or pictures of Chinese zodiac signs such as pictures of dragon, and rabbit.
On the other hand, if one of relatives die, they do not send greetings next year, instead they send grieving cards to notify their close relatives recently die. But they still send cards little earlier than new year so that others won’t send them greeting cards. sending greeting to some who lost their relatives is considered to be bad, so they need to let others know that they can not receive any greetings.