shocking photo of baby elephant tied to a pole spark online campaign .
more than 50,000 have signed petition to have baby elephant , nadia , freed .
marina phuket resort reportedly keeps elephant in tiny enclosure .
` nadia ' is also forced to perform tricks and is ridden by resort guests .
` it is absolutely barbaric , ' says jaime singleton , who started campaign .
comes after phuket resort posted pictures of baby elephant near pool .
party-goers snapped dancing with elephant , and one person seen riding it .