It works. Make screenshots. But make it like any sharpen artefacts. Why? Maybe because wkhtmltoimage running without X? Where try get information? How to smooth screenshot via wkhtmltoimage?
This Firefox and Chromium 800x420: http://s18.postimg.org/xff896gsp/Screenshot_10.png
And this wkhtmltoimage 800x420:http://s9.postimg.org/auikf44st/Screenshot_11.png