Who is a Living Proof?
1: A person(s) who has tested the goodness of God in one way or the others. Psalm 34:8 KJV
 O taste and see that the Lord is good: blessed is the man that trusteth in him.
2: A person(s) who has seen the faithfulness of God firsthand.
3: A person(s) who has evidence(s) of doings of the Lord. Mark 12:10-11 KJV
 And have ye not read this scripture; The stone which the builders rejected is become the head of the corner:  This was the Lord’s doing, and it is marvelous in our eyes?
4: A witness.
For example, John was witness, a living proof of both the earthly ministry of our Lord Jesus Christ and the revelation of Him (the book of Revelation)
5: A testimonial. Acts 4:16 KJV
 Saying, What shall we do to these men? for that indeed a notable miracle hath been done by them is manifest to all them that dwell in Jerusalem; and we cannot deny it.
LIVING PROOF BY SALVATION IN CHRIST
Hebrews 2:3 KJV
 How shall we escape, if we neglect so great salvation; which at the first began to be spoken by the Lord, and was confirmed unto us by them that heard him ;.
Romans 10:9-10 KJV
 That if thou shalt confess with thy mouth the Lord Jesus, and shalt believe in thine heart that God hath raised him from the dead, thou shalt be saved.  For with the heart man believeth unto righteousness; and with the mouth confession is made unto salvation.
2 Peter 1:3-4 KJV
 According as his divine power hath given unto us all things that pertain unto life and godliness, through the knowledge of him that hath called us to glory and virtue:  Whereby are given unto us exceeding great and precious promises: that by these ye might be partakers of the divine nature, having escaped the corruption that is in the world through lust