You can't post pix in the Politics Forum. In other places, you first copy the link/URL of the pic you want to share†, then type your post, position your cursor, and click the Insert Image icon on the toolbar above the Post window you're working in. Then paste that URL/link into the window that comes up, hit the Enter key and finish off your post as usual. The Insert video icon next to it works the same way. Preview frames are in the video itself — or not — you can't create them.
Do us all a favour and keep your image to a reasonable size so we don't have to do a lot of scrolling, and Gifs are cute but get tired awfully fast.
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† That means you can't post your own cat pic unless you make your 'puter a server we can connect to on the Weebs. Or first post Kitty's portrait to a picture-sharing site, then go there and copy it's URL. If you're uncertain, open a new browser window and paste the pic's link into it, to see what you'll force us to look at in your post.