Many architecture papers, posters, etc. require use of the work of others--photos taken by others, writing written by others, etc.  When you create, you're making your own intellectual property (IP).  The challenge--especially in creative fields--is that our intellectual property is often built on ideas (precedents) that came before.  In order to be a responsible IP creator (and even law-abiding, when it comes to copyright laws), you should attempt to cite your sources as thoroughly as possible.

While there are many different standards for citing text-based information, unfortunately, there is no comprehensive or definitive style for citing images.  The major citation styles do have some guidelines, but they currently all fall short of addressing the vast array of sources the internet presents us.  The American Psychological Association (APA) is one of the more user-friendly citation styles, and currently provides the most extensive free advice for overall citations on the internet, here:  https://apastyle.apa.org/.  For more detailed guidance than given by the website, you can access a  print copy at Kennedy Library: Publication Manual of the American Psychological Association: The Official Guide to APA Style.  

The best, most responsible thing to do is come up with a consistent system of captioning your images and referring readers to an image list in your references in the back.