Archival collections can be a rich source of images, especially historic photographs. Many archival institutions have digitized some or all of their photographs and can be found through online databases and webpages:
UBC Library Digital Collections Digitized items from a wide variety of collections held by UBC Rare Books and Special Collections, University Archives and other library branches.
Photographs - ArchiviaNet - Library and Archives Canada Digitized photographs from the holdings at Library and Archives Canada
Library of Congress Prints & Photographs Online Catalog Digitized photographs from the Library of Congress in the United States.
You may also find online photographs by searching these online portals:
West Beyond the West A centralized database to search the digitized holdings of libraries, archives, museums and historical societies across British Columbia
Canadiana Discovery Portal (beta) Provides access to digitized text, images and artifacts from heritage institutions from across Canada.
Library of Congress Digital Collections & Programs
World Digital Library