Can you create a link to a specific message in a conversation in WhatsApp from a Website? No.
Can you create a link to your WhatsApp number from your website, youtube, linkedin, Wix, WordPress? Yes.
Can you create a link to an image shared in WhatsApp from your Website? No.
WhatsApp enables links to phone numbers. That way you can create a link from anywhere (email signature, linkedin profile…) to your WhatsApp number with a predefine message. That link will work from the cellphone and from the desktop.