No (with one exception: HQ accounts can upload a backdrop profile image).
The poster and backdrop images offered on Letterboxd are sourced from TMDB (and Posteritati for additional posters), and there is no option to upload your own image directly to our platform. TMDB accepts user submissions, but please follow the published guidelines when uploading images, as abuse of TMDB’s rules may lead to customization features being suspended on your Letterboxd account. Infringing content includes, but is not limited to, images containing: spoilers, inappropriate nudity, graphic violence, fan art and memes. TMDB submissions can take up to seven hours to appear on Letterboxd due to caching at their end.