Encoding can be done with openssl (openssl enc -base64 -A -in DSC_0251.JPG) or base64 (base64 -w0 DSC_0251.JPG), they are interchangeable.

Similarly, decoding can be done with openssl (openssl enc -base64 -d -A -in encoded-data.txt) or base64 (base64 -d encoded-data.txt).