如何使用jquery ajax和php上传文件（不点击任何提交按钮）

I have a form like this:

<form method="post" class="form_cnvc">
   <p><input type="text" name="f_nm" value="" placeholder="type your first name"></p>
   <p><input type="text" name="l_nm" value="" placeholder="type your last name"></p>
   <div class="dropfile visible-lg">
   <input type="file" id="image_file_input" name="image_file_input">
   <span>Select Images(.jpg , .png, .bmp files) </span>
   </div>
   <p class="submit"><input type="submit" name="submit" value="post"></p>
 </form>

I want that when the user will selects an image, it would be automatically submitted to my PHP page so that I can save it in the database and return an insert_id with the thumbnail of the picture.

I want to do it using jQuery but not able to do so.

PHP code is: