Methods, systems, and devices that support determining whether media data has been altered are described. Captured media data may be segmented into one or more subsets, and cryptographic representations (e.g., hashes) based on the subsets may be written to an immutable ledger, possibly along with metadata and other related data. A block of a blockchain may be created for each entry in the immutable ledger. A set of media data may be validated, if a corresponding immutable ledger exists, based on segmenting the set of media data into one or more subsets in accordance with the segmenting upon capture, creating candidate cryptographic representations (e.g., hashes) based on the subsets, and comparing the candidate cryptographic representations with contents of the corresponding immutable ledger.