You have to use Javascript Filereader for this. (Introduction into filereader-api: http://www.html5rocks.com/en/tutorials/file/dndfiles/)
Once the user have choose a image you can read the file-path of the chosen image and place it into your html.
Example:
<form id="form1" runat="server">
<input type='file' id="imgInp" />
<img id="blah" src="#" alt="your image" />
</form>
Javascript:
function readURL(input) {
if (input.files && input.files[0]) {
var reader = new FileReader();
reader.onload = function (e) {
$('#blah').attr('src', e.target.result);
}
reader.readAsDataURL(input.files[0]);
}
}
$("#imgInp").change(function(){
readURL(this);
});