[j0hnik]

<canvas id="demo" width="500" height="400"></canvas>

	<script>
var ctx = demo.getContext('2d'),
    w = demo.width,
    h = demo.height,
    img = new Image();

img.onload = function() {

    ctx.drawImage(img, 0, 0, w, h);
    download(demo, 'test.png');
    
}

img.crossOrigin = 'anonymous';
img.src = 'http://i.imgur.com/bbQ7uxV.jpg';

/// download canvas as image
function download(canvas, filename) {
    
    if (typeof filename !== 'string' || filename.trim().length === 0)
        filename = 'Untitled';
    
    var lnk = document.createElement('a'),
        e;
    
    lnk.download = filename;		
    lnk.href = canvas.toDataURL();	
    
    if (document.createEvent) {
        
        e = document.createEvent("MouseEvents");
        e.initMouseEvent("click", true, true, window, 0, 0, 0, 0, 0, false, false, false, false, 0, null);
        
        lnk.dispatchEvent(e);
        
    } else if (lnk.fireEvent) {
        
        lnk.fireEvent("onclick");
    }
}

	</script>

5 минут гугла и можно найти множество решений. canvas, base64