Facebook engineer Bob Baldwin, who helped build this feature has said, “I hope this will make threads with friends more expressive and engaging.”
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If you like to add a picture as a comment, all you have to do is to click on the camera icon that is visible in the comment box to the extreme end.
Moreover this feature will be rolling out to every profile page today followed by fan pages on a later stage. In fact i got this feature enabled by default last night and many of my friends are still awaiting the same.
There is no other way round to enable this feature, making you wait until it appears by default.
If this feature is enabled on your profile, then you will notice that this will appear on things you share with friends and majorly when someone shares a picture , album or any URL.
Source : Inside Facebook
Also See : Facebook Introduces Verified Fan Pages and Profiles