The National Archives and the Museum of Australian Democracy At Old Parliament House have developed the website as a Centenary project, in anticipation of 2013, our Centenary year. But the website, with its tantalising invitation to do some rephotographing is already up and going. It employs some 7700 photographs that William James Mildenhall (1891-1962) took of the infant, being-built-while-you-watched, federal capital city. There can be very, very few cities of the world that have such a super record of their infancies.

The website chronicles that ''[Public Servant] Mildenhall went to Canberra in 1921 … and in 1926 was appointed as the official photographer and information officer of the Federal Capital Commission. An enthusiastic amateur photographer, his first work for the government was done in his own time, in return for the cost of photographic supplies … he had pointed out to his superiors that: ''Although there are two departmental cameras held by officers at Canberra, neither of the officers have had experience in outdoor work … [but] I have had 10 years' experience in all branches of photography and have specialised in outdoor work under all weather conditions.''

His career as an official photographer lasted from 1926 to 1935 and we're blissfully lucky as a history-conscious city that the decade of Mildenhall's liberty to roam and capture Canberra coincided with the construction of the provisional Parliament House and all sorts of other exciting spurts of development.

Just looking at the enormous gallery of Mildenhall pictures is very absorbing and the two institutions desperately wanted to share this treasure with the wider world. But wait, the National Archives' Zoe D'Arcy, director of digital and online access, tells Gang-Gang, there's more.

''Essentially we wanted to do an interesting project with the Mildenhall photographs [website]. And I really liked the idea of people being able not only to find the photographs but to do something with them so you're not just looking at a picture and not giving it further thought, but you're actually having to think about where the photograph was taken, about what's changed since then, about what Canberra's become.''

And so the site tickles you with the thought of what fun it is to use the pictures to get out and about in today's Canberra and go and find if you can the places where Mildenhall stood to go about his work of shooting his images. D'Arcy has been doing this and testifies that it is very ''addictive''. The website has a map that you can use to help with your site-fossicking and it's a map to which you can add your own discoveries. Then there's the invitation, with helpful instructions, to ''rephotograph'' the places, the objects, the vistas, to capture what's changed and what is, like the corner of Civic in the before-and-after pictures on this page, eerily the same.

D'Arcy and this columnist enthused together as we went on an online tour of the website within earshot of the Archives' cafe's coffee machine, hissing like a steam engine of the Canberra construction sites of the 1920s.

''When you look at the photographs we're talking about there's all this construction work going on, in the 1920s, so you've got amazing steam engines, you've got horse-drawn tractors. You're looking at buildings being constructed,'' she said.

''There are 100 men putting up the wooden framework for the hall at the Causeway … its just a different way of life that we'd love people to think about, to consider what changes have been made, to actually look at Canberra as that same place, now, to see what's changed. And what's still here. For example the Causeway Hall is, but now its surrounded by buildings [while Mildenhall's Causeway Hall is out in paddocks].''

D'Arcy, on Mildenhall-inspired expeditions, is finding Canberra places she didn't know existed. She hopes you will have similar good fortune. She didn't know of Saint Mark's in Braddon (part of the Charles Sturt University, off Blackall Street, until, using Mildenhall's dramatic photographs of the wreckage of the little RAAF aeroplane that crashed during aerial displays at the opening of Old Parliament House in 1927 (the pilot died and is buried in the cemetery of St John the Baptist's church in Reid) she found the plane had crashed where St Mark's is now. Mildenhall was there in 1927, now D'Arcy has gone there in 2012.

Even if you don't ever make expeditions like hers, the Discovering Mildenhall's Canberra - Photographs From The Birth Of Our Capital is a joy, if you love this city, just as a gallery. You have a miscellany of options. For example enter ''Stromlo'' as D'Arcy did during our session at the Archives, and some of the Mildenhall pictures that come up are of the funeral, up on Mount Stromlo, of the then director of Commonwealth Solar Observatory, Dr W. G. Duffield.

In one photograph Mildenhall has captured pallbearers carrying his coffin against the backdrop of some bleak and wild hillside. If one had to choose the 10 most powerful Canberra-capturing photographs ever taken this one might be among them. Why not go and look at it, now, beginning by Googling ''Discovering Mildenhall's Canberra - Photographs From the birth of Our Capital''?