First, compute the SHA256 hash of the diploma image and check that it is listed in the diploma report. Second, visit the School's website and get the Bitcoin address corresponding to the class of the diploma. Third, visit a Bitcoin blockchain explorer and search the transaction history of this address (paste the address in the search field displayed on the blockchain explorer page). In the transaction history, look for the first (oldest) transaction where the address appears as an input. There should be two outputs to this transaction, one bearing a zero amount and a data hash. Last but not least, compute the SHA256 hash of the diploma report (pdf) file and check that it matches the data hash you just found in the blockchain: that's it !