I would like to reproduce in print a picture taken in the 1920's as part of a project showing the scene as it is today. I know nothing about copyright law and would like to know if I can leagally do this without being sued.
The photo has probably fallen into the public domain, but not necessarily. 1923 is the cutoff year for works falling into the public domain, if the photo was registered but the copyright wasn't renewed, or if published without notice and without subsequent registration within 5 years. Please see the chart linked below. Then see if there's a copyright notice on the photo, and look up the status on the Copyright Office database, also linked below.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
Ms. Koslyn gives a succinct and accurate answer. Another relevant question is where you are getting the photo from. It is possible that the original photo was taken in 1929, but that this image was then in some way cropped, revised, retouched or otherwise modified by a subsequent user, who may as a result of their modification have an independent copyright in their version of the image, even if the original image is now in the public domain. If you subsequently use the revised version you could therefore be committing copyright infringement of the subsequent user's newer work.
Disclaimer: This answer is for informational purposes only and is not intended to serve as legal advice and so should not be used as a substitute for the advice of a competent attorney licensed in your state. This answer does not create an attorney client relationship.