Encrypted JPEG image retrieval using histograms of transformed coefficients

Survey on JPEG compatible joint image compression and encryption algorithms

“…Encryption realised in transformation stage is primarily through replacing DCT with other orthogonal transforms [54–60 ] or encrypting DCT transformed coefficients [61–64 ].…”

“…In [58–60 ], we proposed to realise joint image compression and encryption in JPEG's transformation stage by applying new order‐8 orthogonal transforms alternatively for 8 × 8 blocks’ transformation. The coding efficiency of these new transforms is close to DCT, thus these schemes could achieve good compression and security simultaneously, without breaking the format of JPEG.…”