How to send photos to Chromecast?
There are a handful of different apps you could try, each with varying amounts of features. A few specific examples:


Allcast - Also supports other devices like Roku and Xbox. Casts pretty much any kind of media.
Dayframe - Intended mostly for casting pictures as a slideshow/digital frame.
PhotoCast - Can display photos in a few different styles, including one that plots the location of geotagged images on a map in the background.