Originally this 1956 issue of The Owl was seemingly published without a copyright notice, but even if it was published with a copyright notice of 1956, this issue of The Owl student yearbook would have had to be renewed in 1983. Because this work was originally published before 1964 had to have the copyright renewed sometime in the 28th year. If the copyright was not renewed the work is in the public domain. Renewals for copyrights from 1951 onward (and some, but not all, renewals for 1950 copyrights), as well as original registrations from 1978 onward are available online from the Copyright Office's Copyright Records web site.
Online searches, regardless of year, of Copyright Office's Copyright Records web site for The Owl, editor Joseph A. Banik, the business manager Leo Zelkowitz, or the University of Pittsburgh revealed no renewal entries.
Either this yearbook was never copyrighted or the copyright was not renewed and therefore it is in the public domain according to either criteria.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.
Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (50 p.m.a.), Mainland China (50 p.m.a., not Hong Kong or Macao), Germany (70 p.m.a.), Mexico (100 p.m.a.), Switzerland (70 p.m.a.), and other countries with individual treaties.