Facebook – How to enable photo comments on the Facebook page

Contests/competitions/sweepstakes/etc

must not use Facebook features or functionality as a promotion’s registration or entry mechanism. For example, the act of liking a Page or checking in to a Place cannot automatically register or enter a promotion participant

and

must not condition registration or entry upon the user taking any action using any Facebook features or functionality other than liking a Page, checking in to a Place, or connecting to your app. For example, you must not condition registration or entry upon the user liking a Wall post, or commenting or uploading a photo on a Wall

and

must not use Facebook features or functionality, such as the Like button, as a voting mechanism for a promotion

See Facebook's Promotion Guidlines for the rest of rules and regulations.

When you uncheck Always comment and post on your page as MyPage anything you post on the Page is visible only to some of your friends and people who are visiting the Page profile (i.e. it's not published to the News Feed of the Page's subscribers). Thus, such posts aren't "status" updates.

If you want to publish an actual status update to the Page's subscribers, you need to "Use Facebook as MyPage". The easiest way to do it is to click the triangle in the top-right corner of the screen (on the blue bar next to Home) and select the Page, for which you wish to publish the update.