PHP对Base64的支持非常好，有内置的base64_encode与base64_decode负责图片的Base64编码与解码。

编码上，只要将图片流读取到，而后使用base64_encode进行进行编码即可得到。

我们先来看看编码，直接摘抄网上的代码，示例如下：

$img = './IMG_20180729_203230.jpg';

function base64EncodeImage ($image_file) {
    $base64_image = '';
    $image_info = getimagesize($image_file);
    $image_data = fread(fopen($image_file, 'r'), filesize($image_file));
    $base64_image = 'data:' . $image_info['mime'] . ';base64,' . chunk_split(base64_encode($image_data));
    return $base64_image;
}

$base64_img = base64EncodeImage($img);
echo $base64_img;

得到如下结果(内容太长，我这里截取部分)

data:image/jpeg;base64,/9j/4XfSRXhpZgAATU0AKgAAAAgAEAEAAAMAAAABCZAAAAEBAAMAAAABDMAAAAECAAMAAAADAAAB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==