@Sagar bro, they were also added as a part of 2.1 feature packed software upgrade.
This is how it works, grpahical explanation by XF team:
Here is what i understood:
As you can see aspect ratio can be made smaller and you can add text content beside image itself instead of traditional way, which is below image.
Coming to what i button for - Alt text (alternative text)
You can add a text content explaining the image details there and it will show on accessibility enabled devices (for visually impaired users) also the text will show if you have set your browser preferences to not display any image. Additionally, it will show alt text if you hover cursor on the image.