Follow the docs ios like-button I can create facebook's like button into my app. My code as below:
FBLikeControl *like = [[FBLikeControl alloc] initWithFrame:CGRectMake(200, 110, 250, 250)];
like.likeControlStyle = FBLikeControlStyleBoxCount;
like.objectID = @"https://openmerchantaccount.com/img/8a0e730c-bba3-43f4-9ea1-525c13917980-original.jpg";
[self.view addSubview:like];
Then I can like the page which had objectID as above. But I have a question that, will it (like button) have any value when the image link as above I never post to Facebook page? And what is the purpose of the like button when let users click the like button into my app?(sorry,it maybe a naive question but I really don't understand).
From what I can understand of your question.
The purpose of the like button is that the user "likes" the image, but it is seen as a page. Facebook may display the user's activity to their friends news feeds as well as the user's activity feed.
You can also use the like feature as a small widget on a page to show that "x people like this page including a, b and c" where x is the total number of likes for the objectID and a, b and c being friends of the logged in user. This helps Facebook with advertising based on similar interests.
Just because the page is not posted to Facebook, doesn't mean that it will not appear on Facebook in other means