The data is obtained from the IOI registration system and is accurate at the time of writing. Should any changes/additions occur, I will try to update them in the timely manner.
Where applicable, the photos of the participants of IOI 2015 are also available. Note that permission is required in the registration system to publish any contestant's photo, so where no permission was granted, either a photo from previous IOI(s) was used or no photo is available at all. Again, more permissions may be granted in the future and I will try to update them in the timely manner.
Finally, I have also pulled Codeforces handles from a thread by EXM_KG. I would like to thank him for maintaining it. For the rest of contestants, please feel free to add those in the database if you have such knowledge.