Thanks to Annelise for introducing the University of Southern California's digital library, which includes a good collection of Hong Kong photos.
You can use their advanced search page to use different keywords, and to narrow down the search to a specific date range.
Click on your area of interest to choose from over 17,000 pages about old Hong Kong:
Or choose a popular article:
Upgrade notice: The Gwulo website has recently been upgraded. For details of progress, or to report any problems, please click here. A copy of the pre-upgrade website is still available at http://old.gwulo.com.