Mosaico and Imagemagick
We got it working after having issues with the imagemagick message - we did have it but needed to install php5-imagick - also we were thrown by being on nginx but alpha had been geared towards apache so a bunch of paths weren't working.

we provided feedback/workarounds at https://github.com/veda-consulting/uk.co.vedaconsulting.mosaico/issues/12 which resulted in alpha4 being released. assuming you are using that you might need to open an issue on Veda's github.