To change the Smart Match™ settings for your tree on your family site, go to Family Tree > Smart Matches™.
Next to the name of the tree, click Settings.
To completely disable Smart Matching™ for this tree, un-check ‘enable Smart Matching™’.
Alternatively, to just not allow Photos to be copied through Smart Matches™ for this tree, un-check ‘Allow managers of other sites to copy photos of matched individuals’.
Please note that the Smart Match™ settings are per tree, so make sure that you change them for all trees on your site.