Instagram for iPhone starts rolling out higher quality images in mobile application. Currently the images on an Instagram application displayed at resolution of 640 x 640 pixels. Instagram will soon show users their photos at 1080×1080. The roll out is currently in progress and seems to be limited, for the moment, to the iPhone and Android applications, with no mention being made of the web interface or the beta app on Windows Phone.
Actually this was unveiled by Instagram co-founder Mike Krieger,
Generally the images on Instagram which will displayed at a resolution much closer to that of the original image. As Instagram is currently rolling out higher resolution display and storage, it might take some time for higher-quality images to show up in your feed.