gsnap is a tool which can capture screen (screenshot) base on framebuffer.

Compile for Linux:

$(CC) gsnap.c -ljpeg -lpng -o gsnap

So, you should install libjpeg.so and libpng.so firstly.

Usage:

gsnap <jpeg|png file> <framebuffer dev>

Example:

gsnap test.png /dev/fb0