Shows a single JPEG image in fullscreen using dispmanx.
./showjpeg test.jpg
By default it uses screen 0 and layer -1. To change that, define the environment variables SCREEN or LAYER.
You will need to install libjpeg before you build the program. On Raspbian
sudo apt-get install libjpeg8-dev
Then just type 'make' in the showjpeg directory you cloned from github. If you need a similar tool to display PNG files, have a look at Andrews repository.