"Official stamps were autherized by an Act of Congress, approved March 3, 1873, abolishing the franking privilege. Stamps of special design for each goverment department to prepay postage on official matter were issued July 1, 1873."

The stamps of the Post Office, Department of the Interior, Treasury Department, Post Office, and War Department were issued and used in large quanties, and used copies became readily avaible to collertors. The stamps of the other five departments, Agriculture, Executive, Justice, Navy, and State were much harder to aquire.
In late 1874 or early 1875, Continental Banknote Company produced a Special Printing for the Centennial Exposition, included in that printing were the Departmental stamps. They wer avaible for sale through the Office of the Third Assisitant Postmaster General in Washington, DC. The reissues and special pprintings of the regular issues could be used for postage, but the departmental stamps presented another problem. Their use by officialdon was autherized but prohibited for use by the public. The solution was to overprint the departmentals with the word Specimen.
The demand for used stamps of the Agriculture, Exectuve, Justice, Navy, and State departments soon had nefarious dealers faking cancels on the Special Printing Officials.Most of the fake cancels are simple manuscripts obliterating the overprint, some are much more complex. Some of the fakers were much better at their work than others were! No one knows how many of the Official specimens were so canceled. In their greed, these fakers "canceled" scarce stamps ( most of them issued in quanities less than the $5 Columbian ) and some of those canceled were errors. Below are 17 of these fake cancels, can you spot the two stamps where the faker stepped on his own feet?