Example techniques are described for image-based user authentication. An example method includes receiving, by a host system, a passphrase comprising a plurality of words, the passphrase being provided for authentication of a user. The method further includes generating, by the host system, an image selection grid comprising a plurality of images, each word from the passphrase corresponding to one or more images from the image selection grid. The method further includes receiving, by the host system, a plurality of selected images from the image selection grid. The method further includes storing, by the host system, the selected images as a login challenge for the user.