A service receives a request from a user of a group of users to perform one or more operations requiring group authentication in order for the operations to be performed. In response, the service provides a first user of the group with an image seed and an ordering of the group of users. Each user of the group applies a transformation algorithm to the seed to create an authentication claim. The service receives this claim and determines, based at least in part on the ordering of the group of users, an ordered set of transformations, which are used to create a reference image file. If the received claim matches the reference image file, the service enables performance of the requested one or more operations.