The Ristretto Image Viewer is an application that can be used to view, and scroll through images.
It can be used to run a slideshow of images, open images with other applications like an image-editor or configure an image as the desktop wallpaper.
This manual describes how you can use Ristretto, and how you can configure it to your preferences.
When experiencing bugs in Ristretto, your way of helping things getting fixed is to report a bug about it in bugzilla. Note: For this you will need to have/create an account.