Facebook have been trying to provide new facilities to its users as it's users growing up very rapidly.As a part of their effort, they have introduced new facilities called Facebook Picture Comment. So now and on users will not only can comment on other post, they can post Picture on others post.
The feature was created by Bob Baldwin and his team at one of Facebook's popular hackathons. By the new features, you will see a Camera icon into the comment section. See the picture below.
By clicking on that camera, you will be able to upload a picture. So you can post something to someone's post not only in a text mode, but also in a graphically mode.So when you click and upload the photo, the photo will be inserted as a comment on the post.However at this time this facility is only for one picture.Which means you can upload only one picture at a time.
This feature is available for the web version.It is also available for mobile desktop version.Right this moment, it is not available for mobile applications which will be available later.
This feature supports most of the image format like JPEG,PNG,BMP etc but it is not supported the GIF format.
As this is a new feature, it might be not available to your profile,if so do not need to be worry. It will be in your profile very soon.