This is a Photo Gallery Filled icon. We've made it in iOS style, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 12,800 icons, all in the same style and quality.
The Stack of Photos icon is made up of three squares placed in a staggering order. You can see the entire first square and then the second peeks to the right and beneath the first and the third extends in the same position beyond the second one to create a fan appeal. Each of the squares has a smaller square inside. You can only see the picture in the top square, which is the silhouette of a person.