exif_imagetype() reads the first bytes of an image and checks its signature. When a correct signature is found a constant will be returned otherwise the return value is FALSE. The return value is the same value that getimagesize() returns in index 2 but this function is much faster.
The following constants are defined: 1 = IMAGETYPE_GIF, 2 = IMAGETYPE_JPG, 3 = IMAGETYPE_PNG, 4 = IMAGETYPE_SWF, 5 = IMAGETYPE_PSD, 6 = IMAGETYPE_BMP, 7 = IMAGETYPE_TIFF_II (intel byte order), 8 = IMAGETYPE_TIFF_MM (motorola byte order), 9 = IMAGETYPE_JPC, 10 = IMAGETYPE_JP2, 11 = IMAGETYPE_JPX.
This function can be used to avoid calls to other exif functions with unsupported file teypes or in conjunction with $_SERVER['HTTP_ACCEPT'] to check whether or not the viewer is able to see a specific image in his browser.
Note: This function is only available in PHP 4 compiled using --enable-exif.
This function does not require the GD image library.
See also getimagesize().