Can one open a picture or video after Shabbos from social media of a Jew who posted it on Shabbos?
You may open it after Shabbos after the amount of time it takes to post such a picture or video after Shabbos elapses, which is literally a few seconds after Shabbos.
See also here:
However, if you believe that by not opening it, the individual will refrain in the future from sending it to you on Shabbos, you should indeed not open it.
If it’s a picture or video of an event that happened on Shabbos, other rules might apply. See here:
#18295