These are postage stamps commemorating the 100th and 150th anniversaries of the Emancipation Proclamation.
It’s hard to imagine there was a time when stamps only cost 5¢. And I say that as someone who is over 55 years old.
The blog for the Smithsonian National Postal Museum, Pushing the Envelope, has details of the First-Day Ceremony for the Emancipation Proclamation Commemorative Stamp. It also has some interesting stories and images about Postal Service commemorations of the Emancipation Proclamation, such as this one: