The Spanish expression, "fotos de hombres en boxer," translates into English as "pictures of men in boxers." Although there is no adjective directly following the word fotos, it is worth noting that the noun is feminine, although it ends in the letter "o."
The Spanish word fotos is the plural form of the noun foto. By following the noun fotos with the phrase "de hombres," the expression denotes that the pictures are of men. Furthermore, the phrase, "en boxer," translates into English as "in boxers," even though the Spanish noun in the expression is a singular one. This semantic rule is one of the big differences between English and Spanish.