like button

This is not really a WordPress question, it is a Facebook/html/css question, it just happens that you have a WordPress site.

You will find out how to create the code here:
https://developers.facebook.com/docs/plugins/like-button

You will have to place this code after every image.

You will then have to style the button with css to position it exactly where you want it and style it how you want it to look.

Then what is it’s functionality? What happens when a user clicks it? There is no “code or something” to add to a photo to create the custom functionality you are asking. Will it save a cookie on the user’s machine? Will it add to a like counter? Will this be saved in the database?

You question is VERY broad and offers no explanation.