How to Extract Image Type from Base64-Encoded String in PHP Using FileInfo?

Detecting Image Type from Base64 String in PHP

One may encounter scenarios where access to the original image file is limited, leaving only a base64-encoded string representation. Determining the image type from such a string can prove challenging. While the imagecreatefromstring() function creates an image resource from a decoded string, it conceals the original image type information.

Solution: Utilizing FileInfo

FileInfo offers a viable solution to this problem. By employing its finfo_buffer() method, one can retrieve the image's MIME type directly from the base64-decoded string. This method takes two parameters: an open file handle (obtained using finfo_open()) and the raw image data.

Example Code:

<code class="php">// Encoded base64 string
$encoded_string = "....";

// Decode the string
$imgdata = base64_decode($encoded_string);

// Open FileInfo handle
$f = finfo_open();

// Determine MIME type
$mime_type = finfo_buffer($f, $imgdata, FILEINFO_MIME_TYPE);</code>

The $mime_type variable will now contain the image's MIME type, such as "image/jpeg" or "image/png." This information can then be used to determine the appropriate file extension for saving the image.

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