how to upload image in html

i can upload image but when i did not upload it need store null value how pass null value.

 when i didnot call click upload means its need send null value how to do this.

 

function readURL(input) { if (input.files && input.files[0]) { var reader = new FileReader();              reader.onload = function (e) {                 $('#blah') .attr('src', e.target.result) .width(150) .height(200); };              reader.readAsDataURL(input.files[0]); } }