CW Image Optimizer requires exec()

I’m getting the following error message after installing the plugin

CW Image Optimizer requires exec(). Your system administrator has disabled this function.

Warning: exec() has been disabled for security reasons in /home/xyz/public_html/wp-content/plugins/cw-image-optimizer/cw-image-optimizer.php on line 67

https://www.ads-software.com/extend/plugins/cw-image-optimizer/