Matryoshka dolls are a set of wooden dolls of decreasing size placed one inside another. What's the final one? Image: this
By the name of the file and description I thought that there could be files embedded within this file so from my previous experience I know that there is a 'matryoshka' command within binwalk which can be used with -M.
So I typed
binwalk -e -M dolls.jpgin the terminal and navigated till I found something intresting and I did, I found a flag.txt in the directory:
C:\Users\MAIN\Downloads\_dolls.jpg.extracted\base_images\_2_c.jpg.extracted\base_images\_3_c.jpg.extracted\base_images\_4_c.jpg.extracted
whic gave me the flag:
picoCTF{e3f378fe6c1ea7f6bc5ac2c3d6801c1f}