WWI era photographs (and others) can be found on-line as well at Library and Archives Canada. Here is the main search page:
Search the database - Photographs - ArchiviaNet - Library and Archives Canada
and don't forget to click the little box if you only want the lists that have images on-line otherwise you get the complete list of all those in hard copy only format.
For example. Sir Douglas Haig in his car at Amiens in 1918:
