ContactOwner will allow visitors to send the website owner an email.
ContactOwner is a module for Gallery 3 which will allow visitors to send email messages to the website owner and/or the person who uploaded the item they are currently viewing.
This module may be downloaded from the Gallery forums here.
To install, extract the "contactowner" folder from the zip file into your Gallery 3 modules folder. Afterwards log into your Gallery web site as an administrator and activate the module in the Admin -> Modules menu. Once activated, you will have and Admin -> Settings -> ContactOwner Settings option. Visit this screen to configure the module.
This module uses Gallery's built in Sendmail code. To configure this, copy modules/gallery/config/sendmail.php to application/config/sendmail.php and edit the file to set the from and reply_to addresses.