First of all, I aplogize because I missed the last reply to this thread.
To post a picture in FB you just have to write a new topic attaching your image. You can do it in Twitter by writing to @PixInsight and clicking in the bottom left camera icon to attach the picture.
As far as PixInsight is a FB page and not a fisical person, the way to be linked to the page is just by liking it. In Twitter you add @PixInsight in the same way you add any other person.
Javio