Default WordPress functionality allows you to disable comments globally, or limit them to logged in users etc but it does’t allows you to select post types where you want to disable comments. This tutorial is on new WordPress plugin that allows you to disable comments on selected post types including default post types like media, pages and other custom post types created by you.
Install and activate PMC Disable Comments. Upon activation visit your admin area Dashboard -> Settings -> Discussions, scroll down to the very bottom of the page and choose the Post Types for which you want to switch off comments. That’s all.