PHP Determines whether a picture is formatted as JPG

In fact, many of the methods are very simple, such as

$_files[' userfile ' [' type '] is judged before the file is uploaded.

There is also a getimagesize--get the image size and getimagesize return and the parameters are as follows.

Returns an array of four cells. Index 0 contains the pixel value of the image width, and index 1 contains the pixel value of the image height. Index 2 is the tag of the image type: 1 = gif,2 = jpg,3 = png,4 = swf,5 = psd,6 = bmp,7 = TIFF (Intel byte order), 8 = TIFF (Motorola byte order), 9 = jpc,10 = jp2,11 = jpx,12 = jb2,13 = swc,14 = iff,15 = wbmp,16 = XBM. These tags correspond to the newly added imagetype constants of PHP 4.3.0. Index 3 is a text string with the contents "height=" yyy "width=" xxx, which can be used directly for the IMG tag.