Abstract: Differentiating between human interaction and computer interaction using a natural perception of human eyes to identify human users. One or more images may be displayed within one or more test fields on a web page. The one or more images themselves, or a duration for which they are presented, may cause a human eye to not see something that is in the images or to see something that is not in the images. Input may be received from the user identifying all images that are perceived by the user. A determination may be made that the user is a human user based on what the user identifies. Access to another web page may be granted to users who are determined to be human and denied to users that are not determined to be human.