I want to post images to my website and social media. But I don't know how will protect my images by to others. I know it can't prevent downloading the images.
But how I can protect or have a proof that I created those images.
If you want to have a bullet proof alibi for creation date then submit the file to yourself in registered mail, and keep the letter sealed. This can then be used in court of law.
However this does not protect you from any plagiarism claim. And off course you need to be willing to see their bluff.
Depending on what you make and where you put it you should use watermarks over the whole image. That would be the safest way to keep people from editing your picture. If you take photos watermark in one way ruins photo so photographers use signatures on them - don't put them in corner or edge because sometimes people will go so far to cut out that part; but don't cover the main part of the photo.
After all that you can't really 100% protect your work.