ecc to jpeg conversion is most likely searched by users that had their pictures or photographs encrypted with some ransomware and wonder how to recover these back, since changing file extension back does not work.
Renaming extension to .ecc is known to be done by TeslaCrypt / Cryptolocker ransomware and you have to look for recovery tools for these particular types. TeslaDecoder utility (you can download it from Internet) might perhaps help you out with this, but you can probably find several such tools on the Internet.
Updated: August 31, 2023