Just try NPB, it works great, But when there are new photo added, the NPB load the new images and put it into the left hand side (likely index 0, since you won't use negative index to confuse yourself), and the rest of the older images just shift to the right. When there are many new photos, NPB just waste time shifting photos. It waste battery and prevent user from using it at that moment.
My suggestion is that the oldest image place on the left (starting from index 0), and the latest images add on the right hand side.
For example, I have 1000 images in my phone, and now I have one new image. AND NPB load this latest image to the right hand side (index 1001). No shifting require. Greatly improve performance and battery
Every time NPB open, it just jump to the last known total image number, in the case above, NPB will go to index 1001 to show the latest image.
Last, it will be great to add a indicator to tell NPB are loading new photos, and a time line function which tell which year / month the image was.