Mayan_Mind_Reader app for iPhone and iPad

This app creates the effect of Quetzalcoatl, the Mayan feathered serpent, reading your mind. You freely pick a number and use it to select a Mayan day-image or glyph from the Tzolkin, a 260 day period. There are 20 day-images that are combined with the numbers 1 - 13. You concentrate on the image you selected and when ready, you proceed to the next page. After a short pause, while the Quetzalcoatl concentrates, your image appears along with its Mayan name. The Mayan day names are: Imix, Ik, Albal, Kan, Chikchan, Kimi, Manik, Lamat, Muluk, Ok, Chuwen, Eb, Ben, Ix, Men, Kib, Kaban, Etznab, Kawak, and Ajaw. You have the option to try it again as many times as you wish.
The Tzolkin calendar is combined with the Haab, a 365-day solar calendar, to produce a period of 18,980 days, approximately 52 solar years. This calendar is still in use in the Guatemalan highlands and in Veracruz, Oaxaca and Chiapas, Mexico.
The puzzle is to figure out how this app can identify your image every time.