A computer-implemented method for differentiating between human interaction and computer interaction using a natural perception of human eyes to identify human users, at least a portion of the method being performed by a computing device comprising one or more processors, the method comprising:
- displaying within a test field on a first web page a first image and a second image to a user, wherein the first and second images are displayed for durations that cause a human eye to merge the first and second images together to create a merged image, wherein the first image displays a first character, the second image displays a second character, and the merged image includes both the first and second images together;
- receiving input from the user identifying what is displayed within the test field;
- determining that the user is a human user when the user identifies the merged image as displayed in the test field;
- granting access to a second web page to users who are determined to be human;
- and
- denying access to the second web page to users that are not determined to be human.