Verifying Adwords Conversion Code

By using this code on_sent_ok: "var img = new Image(); img.src='####INSERT HERE THE GOOGLE CONVERSION IMAGE SRC####'" it looks like AdWords can not verify the conversion code.

Could someone confirm that? And yes, I did insert my own conversion image src. 😉

So, the best option would still be to just add a thank you page and add the proper conversion code there?

https://wordpress.org/plugins/contact-form-7/