I don't know about the stills from videos but I do know Pixsy is not much use with LinkedIn takedowns. I had an image on sale in Alamy used in several places on LinkedIn and this was picked up by Pixsy which was very useful. However, a Pixsy case requires confirmation from the agency that no licence has been sold and that you remove the image from sale which may be too much of a sacrifice just for a LinkedIn use.
I took it up with Alamy who said they were unable to act with social media sites (no explanation why) but they were helpful in getting payment from a large media group who had also used the image. I completed the LinkedIn copyright violation form myself and promptly received a reply saying they would deal with it under their publishing rules. Nothing happened and the images are still used in LinkedIn.