After trying to generate a random image ourselve with image magic with:

    ${imagemagick:location}/bin/convert -size 6x6 xc: +noise Random \( -clone 0 -flip \) -append \( -clone 0 -flop \) +append -scale 128x128 $${:location}

I gave up and just download an image from gravatar, but ignoring errors
if any to comply with the "instanciation should work offline" rule.