Link photos to available social media from unlisted gallery

Hello everyone !
I need to share a photo to the social media available in SmugMug (Facebook, Twitter and Google+) and I need to do it quite often.
When I do so, clicking the appropriate link for Facebook for example, what I see later in this social media is the hole gallery (which is unlisted !) while I want to show only the photo, itself and nothing else !
The image in Facebook is too large, and is not showing completely. Instead it shows truncated/cut !
How to overcome these two problems, please ?
Thank you !
All the best ! ... António Correia - Facebook
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You may want to use the photo share option versus the social share options.
In that same share panel, choose photo instead of social. Then select a size and then copy the embed code that is created. This allows you to share just a photo, at a specific size, and not have it linked back to the gallery in any way.
Thank you Kelly

That I already know and it is not what I want.
I thought that sharing an unlisted image under Social would post it directly to the chosen social media available, without any extra work. And not showing the hole gallery !
I even thought it would fit the image to the desirable size of the chosen Social media...
I do not know what I am missing here.