You'll need to check with the owner. To find out the owner, first make sure you're on the Gwulo website page for that photo. It'll have "media" in the url, eg: http://gwulo.com/media/15894
Check any notes below the photo to see if it mentions the photo comes from a third-party, eg from one of the University archives. If that's the case you'll need to contact them.
Otherwise you'll need to contact the contributor who added the photo to Gwulo. Look above the photo and you'll see a line of text in a small font like this:
Submitted by harryhktc on Mon, 09/22/2014 - 22:01
it means that the photo was uploaded to Gwulo by the contributor with user name "harryhktc". To contact them, please write the email you want to send them, but send it to me:
and I'll forward it to them for you. Please include a list of link(s) to the pages of the photo(s) you are interested in, and if you're requesting photos from multiple people please send me one message per person.
Here's a suggested format for your message:
Subject: Request to use your photos
Dear Harry << replace with owner's name
I would like to use the following photographs that you have uploaded to Gwulo.com:
- http://gwulo.com/media/19891 << provide links to the photos
They are just what I'm looking for to illustrate a project I'm working on. <<Give a description of your project, whether it is commercial or not, and how you'll use the photos>>.
Please can I have your permission to use your photos for this project?
I plan to note "Photos courtesy of Harry << change", and include the links shown above. If you'd prefer something different, just let me know.
Thanks & regards,