How to check if I am inside the WP Theme Customizer preview?

Question

I have some elements showing on the home page that I do not want to display in the Theme Customizer preview window. Is there a simple check in PHP that I can use for that ?

For example:

<img class="background" src="<?php echo $background ?>" <?php if(is_wpThemeCustomizer()) echo 'style="display:none"' ?>/>

I could do it in javascript using the js file that is enqueued only in this case, but I would like to use PHP, or even better : CSS. Is it possible ?