Use Terminal to base64 encode an image
Generate base64 version of an image:
openssl base64 < path/to/file
Do the same, but remove line breaks:
openssl base64 < path/to/file.png | tr -d '\n'
Do the above, but copy the result to the clipboard:
openssl base64 < path/to/file.png | tr -d '\n' | pbcopy