You can find below articles, which are mainly focused on Vision-Based Localization for Leader-Follower Formation Control:

1. Article Vision-Based Localization for Leader–Follower Formation Control

2. Conference Paper Vision-based Localization of Leader-Follower Formations

You can find below articles:

1. Leader–follower formation control of underactuated autonomous underwater vehicles

2. Leader–follower formation control of nonholonomic mobile robots with input constraints

Dear Sathishkumar Moorthy

There are few code available regarding this subject.

If you are interested in the learning aspect, this article is good:

Learning Vision-based Flight in Drone Swarms by Imitation

IEEE ROBOTICS AND AUTOMATION LETTERS. PREPRINT VERSION. ACCEPTED JULY, 2019

Another very good article - WITH CODE (at least should be released soon): a drone is following a target with an AprilTag - the target can be the considered as the leader.

Fast-Tracker: A Robust Aerial System for Tracking Agile Target in Cluttered Environments

https://arxiv.org/pdf/2011.03968v1.pdf

code:https://github.com/ZJU-FAST-Lab/Fast-tracker

Regarding source code, another place to look at is:

Multi-robot Systems (MRS) group at Czech Technical University in Prague

https://github.com/ctu-mrs

Please look at the video that may fit your need: https://www.youtube.com/watch?v=Ax3ONfo1hMA

Best