Stay with 7.19 or hack 7.22 (to avoid the "itok" issue)
No need to hack, just add the following line to your settings.php file:

$conf['image_allow_insecure_derivatives'] = TRUE;    


Source

That will stop the itok parameter from being used.

It's even been wrapped in a module if you don't fancy editing settings.php.

Image Allow Insecure Derivatives


  Provides a user interface to allow Drupal to bypass the token security check when generating image derivatives.


As a side note, trying to hide your site's identity as being a 'Drupal' site is pointless. It's known in the field as 'Security through Obscurity', and it's a waste of resources that could be spent solving real security or performance issues.

See How can I obscure what I am using to run my site? for a more in-depth explanation.