Validate Extension .jpeg,.jpg,.png,.tif,.tiff,.bmp

$('INPUT[type="file"]').change(function () {

var ext = this.value.match(/\.(.+)$/)[1];

switch (ext) {

case 'jpg':

case 'jpeg':

case 'png':

case 'gif':

$('#uploadButton').attr('disabled', false);

break;

default:

alert('This is not an allowed file type.');

this.value = '';

}});

For the front-end it is good convenient to put 'accept' attribute like as.
       accept="image/jpg,image/png,image/jpeg,image/gif" 
/>