In the gurdwara you will often find pictures of one or more of the ten Sikh gurus.  The word ‘guru’ means teacher.  The ten gurus were the ten main holy teachers of Sikhism.  The first guru, Guru Nanak started Sikhism in about 1500 CE (AD).  Just before the 10th human guru, Guru Gobind Singh died in 1708 CE, he said that there was no need for any more human gurus.  The Guru Granth Sahib, the Sikh holy book would be the only guru needed from now on. 

The pictures of the gurus on the walls of the gurdwara remind Sikhs that they should follow their teachings and live as the gurus lived.  Sikhs may also have these pictures on the walls of their home.  However, Sikhs would never say their prayers to the gurus.  It is only God that they worship.