How do you Encryption?

Encoding of data to prevent unauthorized access to data or to be more descriptive: Encryption refers to algorithmic schemes that encode plain text into non-readable form or cyphertext, providing...

I think you may be confusing synchronous/asynchronous communication with symmetric/asymmetric key encryption. Not being certain which you are inquiring about, I'll try to explain each...

Yes. Public Key encryption (or asymmetric encryption) requires a pair of keys; a public and a private key for exchanging data in a secure manner.

Basically Image Encryption means that, convert the image into unreadable format.

putting a password on a file, or coding the data so to anyone able to open it is unable to read it unless they decode it. usually decoding is very hard and almost impossible for those who dont posess...