Congress President Sonia Gandhi and Vice President Rahul Gandhi on Monday attended the inauguration of a photo exhibition on late Prime Minister Indira Gandhi's life to mark her birth centenary celebrations.Sonia daughter Priyanka Gandhi Vadra was also present at the photo exhibition.The theme of the photo exhibition was "Indira - A Life of Courage", which was inaugurated at Swaraj Bhawan in Allahabad.Speaking at the inauguration, Sonia said: "The biggest concern of Indira Gandhiji was to build a strong and developed nation."Earlier, speaking at the Indira Gandhi Centenary Celebrations at the Vigyan Bhavan last week, Sonia said the late Prime Minister was not only her mother-in-law but also a mother, mentor and a guide to her.