Aperi'Solve is an online platform which performs layer analysis on image. The platform also uses zsteg, steghide, outguess, exiftool, binwalk, foremost and strings for deeper steganography analysis. The platform supports the following images format: .png, .jpg, .gif, .bmp, .jpeg, .jfif, .jpe, .tiff...

the image in this tweet is also a valid ZIP archive, containing a multipart RAR archive, containing the complete works of Shakespeare.

Source code. This one is also a PDF : SOURCE.PDF.ZIP.JPG

From: http://taint.org

Awesome trick ! And the source code is in Python