Chitragupta means collection of pictures. It is believed that Chitragupta examines the good and

Legend
There is a legend associated with Chitra Poornima involving Lord Indra, the king of Gods, and his Guru Brihaspati. Lord Indra and Brihaspati once had an argument. As Indra failed to respect Guru, he stopped advising Indra who started committing sins in the absence of Guru. Days passed and Brihaspathi returned to his duty. He advised Indra for a pilgrimage to the earth to lessen the burden of sins. During the pilgrimage, Indra realized that he had been redeemed from the sins. He found a Shiva lingam under a Kadamba tree and believed that Lord Shiva had helped him in relieving his sins. Following this, he started worshipping him. He worshipped Lord Shiva with a golden lotus which he found from a nearby pond.
This was believed to be happened on a Chitra Pournami day and the place was Madurai in South India. Devendra puja is held during Chitra Pournami day in Madurai Meenakshi Amman Temple, commemorating the event.
The Mangaladevi Temple located at Kumily in Idukki, Kerala also celebrated Chithra Pournami festival with much religious fervor. Mangala Devi Temple is build in Pandya style of architecture is dedicated to Kannagi or Kannaki Amman, the main character of the South Indian epic Silapathikaram. The temple is around 2000-years-old and remains closed for the entire year except for Chithra Pournami Festival. Hundreds of pilgrims from Kerala and the nearby state of Tamil Nadu visit the shrine during the festive occasion.
source:http://www.hindudevotionalblog.com/2009/05/chitra-pournami-on-may-2009-chitirai.html