There are no copyright marks or statements on either side of this card as seen at photo links.
It was created for distribution to the show's viewers; copies were distributed in response to fan letters, photo requests, etc. The image was meant to attract attention and publicity for the show. The aim of this image was exactly the same as the publicity shots/stills done in the film industry.
The rear of the photo clearly indicates that the ultimate source for it was WGN-TV.
Garfield Goose and Friends left the air in September 1976. The retirement of Ned Locke as Ringmaster Ned created a need for a master of ceremonies on the Bozo's Circus program. Frazier Thomas was asked to assume this role. When he did, he brought his cast of puppet characters with him and the two shows were "merged" in a way. In January 1981, Thomas' puppets were off the air due to a Bozo's Circus format change. It moved to mornings in 1980, and took over the time slot of Ray Rayner and His Friends at the time the puppets were no longer on the air.
This postcard was produced to herald the "merger" of Garfield Goose and Friends with Bozo's Circus in 1976.
A search was done on Bozo, with no results found that pertains to the Chicago version of the television show, but to various items marketed by Larry Harmon, creator of the Bozo the Clown character. These items are generic in the respect that they do not deal with a specific local production of the Bozo show, but to the character in general.
They reveal that WGN-TV renewed no copyrights to this image or any collection of images or any collection of material that might encompass this image.
There is no evidence that WGN-TV claims copyright on the image.
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.