Drop Canon CR2, Nikon NEF, Sony ARW, DNG, Olympus ORF, Panasonic RW2, Pentax PEF or Fujifilm RAF files. The JPEG preview the camera saved inside each one is found, turned upright and shown at its own pixel size — ready to save as JPG.
The camera's preview, not a RAW development
A RAW file holds the sensor's data, which has to be developed — demosaiced, white-balanced, tone-mapped — before it is a picture. Cameras also store a ready-made JPEG inside the file so their own screen can show it. This page finds that JPEG; it does not develop the sensor data, and it says so on every result. The preview carries the camera's own processing: its white balance, picture style and noise reduction at the moment of shooting.
Many cameras store a preview at or near full size; some store a smaller one. The page prints the preview's real pixel size so you know exactly what you are getting before you save.
How it is found
CR2, NEF, ARW, DNG, ORF, RW2 and PEF are built on the TIFF structure: this page walks the file's directories and sub-directories for embedded JPEGs and picks the largest. RAF keeps its preview's position in the file header. When the structure points nowhere useful, the file is scanned for embedded JPEGs. The camera's orientation is applied, so a portrait shot comes out upright.
You can save the preview exactly as the camera stored it, byte for byte, or as a JPEG or PNG written here (the JPEG searched to visually identical, 0.990 at 512 px). Canon's newer CR3 format is not read yet; the page says so.