"The image corresponding to the emoticon may be an image of the user with an expression similar to the expression conveyed by the detected emoticon," the patent said.
"The image might also be any image the user has preselected to represent the expression conveyed by the detected emoticon".
Facebook might also prompt users to select an image from a bank of pictures.
The U.S. social networking giant already has some artificial intelligence-powered software that can recognize faces. It's unclear whether this could be the technology powering this latest step.
Facebook is not the first company to develop customized emojis. Messaging startup Slack allows users to upload an image that can be turned into an emoji.
The latest patent highlights Facebook's push to make the service more personal. Earlier this year, the company unveiled new "reaction buttons" that allow people to react with different emotions to a post.