This is an entry in our Disneyland 101 Glossary: Disneyland Resort definitions in under 101 words, from Mouse Brief.
PhotoPass Lenses work with your mobile device to add Disney park themed augmented reality effects to your photos. Examples of these effects include: bubbles reflecting your face, a character like Mickey peeking over your shoulder or turning your skin blue to make you resemble Genie (from Aladdin). These lenses are (at the time of this writing) only available with the purchase of Lightning Lane Multi Pass. The lenses are accessed through the Disneyland app.
For specific information about Lightning Lane Multi Pass, check-out our guide here.