Images shared on social media are mostly not watermarked.. ie twitter, pinterest

I just noticed that images I’m sharing to social media are not watermarked.

For example,

The image I posted at http://www.lbiviews.com/2018/02/acme-bar-beach-haven/ is watermarked properly.

However,

When I look at pinterest, I can do a save as and then download it without the watermark.

I believe this link will take you to the pinterest pin https://www.pinterest.com/pin/664843963714645628/

I also noticed that in a twitter share, one image was watermarked and the other was not.

The first image of the snake is not watermarked but the second is. Both images are set to ‘large’ in wp which, for me, is 800 x 600

The snake post is at http://www.bucksviews.com/2018/02/a-snake-in-the-pool/

I used sassy social share for the pinterest pin and twitshot for the twitter share. IOW, I don’t think that the problem lies withe the share buttons.

WP version Version 4.9.4
Image watermark Version 1.6.4

I do NOT have image watermark set to watermark full sized images. If that is the issue I can easily change that so that image watermark watermarks full sized images.

I’m not worried about facebook at this time because I don’t think you see save image until you click on the pic. When you click, it takes the viewer to my sits.

My questions:

* should the images showing in social media and twitter show the same watermark as on my site. ?
* If so, how do I get images shared on social media to be watermarked.

thanks

chris