resizeImage

function resizeImage(f) {

    var file = f,
        fileType = file.type,
        reader = new FileReader();

    reader.onloadend = function() {
      var image = new Image();
          image.src = reader.result;

      image.onload = function() {
        var maxWidth = 250,
            maxHeight = 250,
            imageWidth = image.width,
            imageHeight = image.height;

        if (imageWidth > imageHeight) {
          if (imageWidth > maxWidth) {
            imageHeight *= maxWidth / imageWidth;
            imageWidth = maxWidth;
          }
        }
        else {
          if (imageHeight > maxHeight) {
            imageWidth *= maxHeight / imageHeight;
            imageHeight = maxHeight;
          }
        }

        var canvas = document.createElement('canvas');
        canvas.width = imageWidth;
        canvas.height = imageHeight;

        var ctx = canvas.getContext("2d");
        ctx.drawImage(this, 0, 0, imageWidth, imageHeight);

        // The resized file ready for upload
        finalFile = dataURItoBlob(canvas.toDataURL(fileType));
      }
    }
    reader.readAsDataURL(file);
}