https://www.activestills.org/js/captcha.js?num=5

1var captcha_bg_color = "rgb(191, 157, 94)";
2var captcha_text_color = "rgb(93, 93, 93)";
3function DrawPixel(canvas, ctx, color, x, y)
4{
5	ctx.fillStyle = color;
6	ctx.fillRect( x, y, 1, 1 );
7}
8function GetRandomCode(chars_count)
9{
10	var code = "";
11	//var possible = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
12	var possible = "0123456789";
13
14	for (var i = 0; i < chars_count; i++)
15	{
16		code += possible.charAt(Math.floor(Math.random() * possible.length));
17	}
18
19	return code;	
20}
21function init_all_captch()
22{
23	$(".captcha_image_canvas").each(function(index, element)
24	{
25		var canvas = element;
26		var ctx = canvas.getContext("2d");
27		
28		var code = GetRandomCode(6);
29		
30		var canvas_w = canvas.width;
31		var canvas_h = canvas.height;
32		//alert("canvas_h: " + canvas_h)
33		
34		var canvas_w_vw = ConvertPx2Vw_fixed(canvas_w,1025);
35		var canvas_h_vw = ConvertPx2Vw_fixed(canvas_h,1025);
36		//alert("canvas_h_vw: " + canvas_h_vw)
37		
38		var site_width = window.innerWidth;
39		var new_canvas_w = canvas_w_vw * (site_width / 100); 
40		var new_canvas_h = canvas_h_vw * (site_width / 100); 
41		//alert("new_canvas_h: " + new_canvas_h)
42		
43		canvas_w = canvas.width = new_canvas_w;
44		canvas_h = canvas.height = new_canvas_h;
45		
46		var total_pixels = canvas_w * canvas_h;
47		var pixels2draw = Math.floor(total_pixels / 2);
48		
49		var pixels_locations = [];
50		for(var i = 0; i < pixels2draw; i++)
51		{
52			var random_x = Math.floor(Math.random() * canvas_w);
53			var random_y = Math.floor(Math.random() * canvas_h);
54			var str_location = random_x + "," + random_y;
55			
56			while(pixels_locations.indexOf(str_location) >= 0)
57			{
58				var random_x = Math.floor(Math.random() * canvas_w);
59				var random_y = Math.floor(Math.random() * canvas_h);
60				var str_location = random_x + "," + random_y;
61			}
62			
63			pixels_locations.push(str_location);
64			
65			DrawPixel(canvas, ctx, captcha_bg_color, random_x, random_y);
66		}
67		
68		var font_size = canvas_h/2;
69		
70		ctx.fillStyle = captcha_text_color;
71		ctx.font = font_size + 'pt arial';
72		ctx.textAlign = 'center';
73		ctx.textBaseline = "middle"; 
74		ctx.fillText(code, canvas_w/2, canvas_h/2);
75		
76		setCookie(cookie_name_captcha + "_" + canvas.id,code,1);
77		
78	});
79}