Добби_Старк,
<!DOCTYPE html>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
</head>
<body>
<input type="file" id="imageLoader" name="imageLoader"/>
<canvas id="imageCanvas"></canvas>
<script>
var imageLoader = document.getElementById("imageLoader");
imageLoader.addEventListener("change", handleImage, false);
var canvas = document.getElementById("imageCanvas");
var ctx = canvas.getContext("2d");
var dx = 0;
var width = 0;
var arrImg = [];
function handleImage(e) {
var reader = new FileReader;
reader.onload = function(event) {
var img = new Image;
img.onload = function() {
width += img.width;
canvas.width = width;
canvas.height = Math.max(canvas.height, img.height);
arrImg.push(img);
dx = 0;
arrImg.forEach(function(img) {
ctx.drawImage(img, dx, 0);
dx += img.width
})
};
img.src = event.target.result
};
reader.readAsDataURL(e.target.files[0])
};
</script>
</body>
</html>