@xrnzaaas said:

I'm currently watching season 2 of The X-Files and it's become very annoying - a lot of the thumbnails show heavy spoilers, like the killer or one of the last scenes of the episode. Were they picked manually and is it possible to replace them with 'safe' pictures? I still like to read the overall synopsis of the episode, but I don't want the pic to ruin the experience for me.

Then read the synopsis on either Wikipedia or IMDb.

No real images on wiki but the descriptions are more detailed.

https://en.wikipedia.org/wiki/List_of_The_X-Files_episodes#Season_1_(1994%E2%80%9395)

Images but I don't think they give away anything (IMHO).

https://www.imdb.com/title/tt0106179/episodes?season=1