How to Detect Image Type from Base64 String in PHP?

PHP String-Based Image Type Detection

Identifying the type of an image encoded as a base64 string can be a challenge in PHP. Traditional image detection methods that rely on file access are not applicable in this scenario. However, there is a reliable solution using FileInfo:

FileInfo's Role in Detecting Image Type

FileInfo provides an elegant way to determine the MIME type of an image from its base64-encoded representation. By using finfo_buffer(), you can decode the base64 string into an image buffer and then pass it to FileInfo for analysis. The FILEINFO_MIME_TYPE flag specifies that you want to retrieve the MIME type, which typically corresponds to the image format.

Implementation Steps

To utilize FileInfo for image type detection:

1. Begin by decoding the base64 string into an image buffer.
2. Open a FileInfo object and specify the FILEINFO_MIME_TYPE flag.
3. Pass the image buffer to FileInfo via the finfo_buffer() function.
4. The resulting $mime_type variable will contain the MIME type, which can be used to determine the image format.

Example Usage

<code class="php">$encoded_string = "....";
$imgdata = base64_decode($encoded_string);

$f = finfo_open();

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

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