Sometime downloaded images not shows in android gallery, don’t be worry your android os and phone is not damaged, than why this happen? The reason is android take little more time to read images as a image file format and than it will transfer images into gallery, but as I said it will take some more time, to quickly fix this problem you have 2 options:
1. First : Go to “Download” folder and access picture from there, but this is not a solution, try second method.
2. Second: Reboot your phone will get all download images in gallery.