I've seen that encrypting an image with AES-CBC then calculating the HMAC-MD5 value for authentication is a somewhat common and sound way to secure data. Alternatively, can I just calculate the CRC of the data, and then encrypt the data+CRC with AES-CBC?
I am concerned about a ciphertext-only attack modifying the data and that data then being decrypted and executed/processed. Can I assume that it is unreasonably difficult to maliciously modify encrypted data in a way that results in the same CRC or modifies the encrypted CRC to match? If that assumption can be made, then is it necessary to also do an HMAC-MD5 calculation of the encrypted data?