Tried steganography tools online first with no results.

• exiftool
• strings
  • base_images/2_c.jpg - this may be the filename hidden in the dolls.jpg
• file
  • The file is in fact a PNG, not a JPG.

Resources ​

• https://dmfrsecurity.com/2021/08/24/picoctf-2021-matryoshka-doll-writeup/