Test images and results of compression benchmarks.
An overview of the benchmark results is maintained here: https://docs.google.com/spreadsheets/d/1LxY78fbm47VmrYGTXkBXXitGjhGl32NsuHPH2QXufgA/edit?usp=sharing
The following article also contains interesting results: http://cloudinary.com/blog/flif_the_new_lossless_image_format_that_outperforms_png_webp_and_bpg