Antialiasing for picture passwords and other touch displays is disclosed. In some embodiments a client device for authenticating a user is operable to obtain a sequence of input actions for an image and obtain a partial hash from a Proof of Knowledge (PoK) server where the partial hash is part of a hash used for authentication of the user. The client device is also operable to calculate a hash for the sequence and determine if a part of the hash matches the partial hash. If the part of the hash matches the partial hash, the client device sends a communication to the PoK server to authenticate the user based on the hash for the sequence of the one or more input actions and obtain a response indicating whether the user is authenticated. In this way, sending some hashes to the proof of knowledge server may not be necessary, saving resources.