The T. Rex sprite was made by randizer_drachen on Reddit.
The Susie, Kris, textbox, as well as text were all made by Toby Fox and/or Temmie Chang (I know she did sprite work for Undertale, so I assume it's the same here?)
I don't know who took the picture I used for Isla Sorna, but you can find it on the Fandom Wiki for Jurassic Park (on Isla Sorna's page).
The Jurassic Park font I used was taken from a picture by elfatimishop on Etsy.