如何检测图像是PNG还是APNG格式？ [重复]

Question

Possible Duplicate:
Can I programatically determine if a PNG is animated?

APNG is backwards compatible with PNG. I opened up an apng and png file in a hex editor and the first few bytes look identical. So if a user uploads either of these formats, how do I detect what the format really is? I've seen this done on some sites that block apng.

I'm guessing the ImageMagick library makes this easy, but what if I were to do the detect without the use of an image processing library (for learning purposes)? Can I look for specific bytes that tell me if the file is apng?

Solutions in any language is welcome.

Answer 1

APNG and PNG files' first few bytes' control can be bypass, easily . So this method isn't secure. User can change file's hex code and pass your this control.