A scan of the back side of the photo is unavailable. However, a different publicity photo for the same film With Six You Get Eggroll (1968) from the same eBay seller has both front and back side scans, which show that the photo was published without a copyright notice. See File:With Six You Get Eggroll (1968) publicity photo of George Carlin.jpg.[a]
Furthermore, front and back side scans from other publicity photos are available below.
None of the above photos have a copyright notice. Thus it is reasonable to assume that this photo also does not have a copyright notice, despite the fact that a scan of the back side is unavailable.
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.
↑The eBay seller was initially requested a back side scan for the George Carlin photo mentioned above. However, the seller did not respond to a subsequent request for back side scans of other publicity photos also available for sale, including the Barbara Hershey photo in question. The other photos requested were:
Uploaded a work by {{unknown|author}} from [https://web.archive.org/web/20230712130547/https://www.ebay.com/itm/394673824573 eBay] ([https://web.archive.org/web/20230712130538/https://www.ebay.com/itm/394673824573?orig_cvip=true original listing]): [https://web.archive.org/web/20230712130444/https://i.ebayimg.com/images/g/YckAAOSwjGxfpPRw/s-l1600.jpg front, JPG], [https://web.archive.org/web/20230712130505/https://i.ebayimg.com/images/g/YckAAOSwjGxfpPRw/s-l1600.png front, PNG] with UploadWizard