In 2014,the Starbucks Company invited people over to decorate the iconic white cups. This attracted around 4000 entries over three weeks. The contest encourages customers in the U.S. and Canada to decorate a Starbucks cup with customized art, take a photo of it, and submit the design through social media using #WhiteCupContest. 

UGC is powerful in this case because everyone is on it (social media , peer reviews , conversation with friends)UGC forms all have in common is that people use them as part of the buying experience to help them make purchasing decisions.

When the contestants came to decorate the cup , once finished , they would had to post a picture of it and tag it by saying  #WhiteCup.By placing the hashtag it makes the topic of interest and facilitate a search for it.That is an example of UGC where , you are using social media techniques in order to make people aware of the project.

Starbucks smartly used the technique ' collective intelligence' as an advantage in order to bring people together, get people involved.By making it aware, people started to share it and this benefits Starbucks by making more profit.
Also Starbucks used the advantage of how the audience nowadays are ' prosumers' which they do not only consume a product but they produce. Now people can take a high quality picture on their phone and post it which is a big difference from the early centuries.