Slicing/splicing/hidden images in movies, TV shows

[I AM WE ARE]

I'm watching this series Marianne on Netflix and there's hidden images flashed in every episode I thought this was illegal to do. Did some Google and it's in other movies as well. How is it legal to do this?

 

[I AM WE ARE]

@Lootpack

 

[Lootpack]

I had started watching this show but never finished it. Is this not part of the chilling imagery shown throughout?

 

[I AM WE ARE]

I had started watching this show but never finished it. Is this not part of the chilling imagery showed throughout?

I'm saying that it happens in more movies than we know. Remember they joked about it in fight club, the infamous penis scene? I'm trying find credible sources about other shows as well