Here we have applied some validations on the selected file, to check it whether it is an image file (jpg, jpeg or png ) or any other file type. Upload File size allowed is 100 Kb.  
Following steps are pointed under this process : 1.  Include jQuery library. 2.  HTML page with upload field. 3.  jQuery Ajax code. 3.  PHP script to store image.    Ajax Code :

url: "ajax_php_file.php", // Url to which the request is send
type: "POST",             // Type of request to be send, called as method
data: new FormData(this), // Data sent to server, a set of key/value pairs (i.e. form fields and values)
contentType: false,       // The content type used when sending data to the server.
cache: false,             // To unable request pages to be cached
processData:false,        // To send DOMDocument or non processed data file it is set to false
success: function(data)   // A function to be called if request succeeds
  PHP code used to store the image :

$sourcePath = $_FILES['file']['tmp_name'];       // Storing source path of the file in a variable
$targetPath = "upload/".$_FILES['file']['name']; // Target path where file is to be stored
move_uploaded_file($sourcePath,$targetPath) ;    // Moving Uploaded file