I found a quite large list of available libraries on Node.JS wiki but I'm not sure which of those are more mature and provide better performance. Basically I want to do the following:
Big plus if the node package works on both Linux and Windows.
Answering my own question
I spent two days digging through Node.js graphics libraries.
<canvas>API. It's a huge plus for a library.
montagewhich does exactly what I need.
I also looked at other libraries from the list but most of them are either very immature or do not suit my use case. I would really like to try migrating to either Node-Canvas or Node-Vips when Node-Waf gets ported to Windows but until then I'll stick to node-imagemagick.