Self-portraits have been made since the earliest times, it is not until the Early Renaissance in the mid-15th century that artists can be frequently identified depicting themselves as either the main subject, or as important characters in their work.
Renaissance self portraits; with better and cheaper mirrors, and the advent of the panel portrait, many painters, sculptors and printmakers tried some form of it. Portrait of a Man in a Turban by Jan van Eyck of 1433 may well be the earliest known panel self-portrait. He painted a separate portrait of his wife, and he belonged to the social group that had begun to commission portraits, already more common among wealthy Netherlanders than south of the Alps. The genre is venerable, but not until the Renaissance, with increased wealth and interest in the individual as a subject, did it become truly popular. [wiki]
One of the most distinguished, and oldest, collections of Renaissance self portraits are in the Vasari Corridor of the Uffizi Gallery in Florence. It was originally the collection by the Cardinal Leopoldo de’ Medici in the second part of the 17th century and has been maintained and expanded until the present time. It is mostly not on view for general visitors, although some paintings are shown in the main galleries. Many famous artists have not been able to resist an invitation to donate a self-portrait to the collection. It comprises more than 200 portraits, in particular those of Pietro da Cortona, Charles Le Brun, Jean-Baptiste-Camille Corot, and Marc Chagall. Other important collections are housed at the National Portrait Gallery (United Kingdom) in London (with various satellite outstations elsewhere), and the National Portrait Gallery in Washington, D.C..
You can find more and detailed information about Renaissance self portraits and self-portraiture at its wikipedia page.