For this tutorial you need :

Mozilla Firefox

Live HTTP Headers -> https://addons.mozilla.org/en-US/firefox...p-headers/

Find an website which allows you to upload .jpg , .png or any other extension

So now once you have found a website , we are going to try and upload .php file

For example if i try to upload BCA.php 

The server rejects the file and says wrong extension 

Now we are going to rename our shell to

Code:
bca.php.jpg

Now try opening the Image , Right click on it and open in new tab

Now go to the upload spot and click browse

Go to the Live Http Headers and run it

The Capture Box should be checked

Now upload the shell , Wait for it to load completely and our bca.php.jpg should come up on the Live Http Headers

Highlight the shell name and click on the replay button

A new windows should popup , now we have to find our shell name for example bca.php.jpg and rename is to bca.php

Now when you have done that click the replay button again

The page should refresh

Now right click on the picture you upload and open in new Tab 

There you go the shell should be there