A gif in the middle of a post, sure. Plastering copyrighted movie images all over your post without sourcing, no. If you look at my movie/tv posts you can see I source them all. Not a single image is ever unsourced unless it is CC0. I am more lax with Gifs as they fall more under fair use similar to memes. They are considered social culture.

Gifs are more under fair use than images because one of the key components of fair use is the fraction of the derivative work. An image is 100% of the derivative work and thus completely stolen if not sourced, but a gif is generally like 0.001% of the original work and fall well below the ~30% guideline.