According to the U.S. Postal Service, stamp designs are voted upon by the Citizens' Stamp Advisory Committee. The committee was created to sift through as many as 50,000 stamp proposals annually and determine which design ideas should move forward in the stamp creation process.
The USPS explains that the Citizens' Stamp Advisory Committee was established in 1957 at the request of the postmaster general. The committee's members are appointed by the postmaster general and meet four times a year to review stamp proposals that meet the USPS's eligibility requirements. The committee has set forth criteria, such as standing the test of time, having broad appeal and being consistent with public opinions, as ways to evaluate proposals.
The USPS reports that proposals must be submitted in writing to the Citizens' Stamp Advisory Committee at least three years before the anticipated stamp release date to accommodate the selection, design and production processes. After a proposal is deemed appropriate, discussion of the proposal is placed on the committee's meeting agenda. The committee can reject a design or forward it to the USPS for further consideration. Once a proposal is finalized, it is assigned to a contracted designer or artist so that artwork capturing the spirit of the proposal and meeting strict aesthetic criteria can be designed.