(Node.js) Watermark an image using ImageMagick from two streams.

nodeWatermark.js

/**
* Dependencies
*/
var fs = require('fs'),
	request = require('request'),
	cp = require('child_process'),
	spawn = cp.spawn;

var image = request("http://medpreps.com/wp-content/uploads/2012/05/cma-practice-test.jpg");
var wm = request("https://github.com/linse/Gibberbot/diff_blob/f096f6d94b3fb745975ea5f61f5a43b47098598b/res/drawable/droid_watermark.png?raw=true");

// Composite is one of the file that make up image magick.
// The second argument, `+200+200` represent the location on the image where to put the watermark (x,y from top left).
var args = ['-geometry', '+200+200', 'wmPipe', 'basePipe', '-'];
var composite = spawn('composite', args);

/*
* basePipe and wmPipe are two name unix pipes.  You can create one with `mkfifo basePipe && chmod 777 basePipe`
*/
image.pipe(fs.createWriteStream("./basePipe"));
wm.pipe(fs.createWriteStream("./wmPipe"));

// Pipe the image magick output to a file. Could just as easily pipe it to a http response or any other stream.
composite.stdout.pipe( fs.createWriteStream("out.jpg") );

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