如果从.png重命名为.jpg，请检查图像类型

Question

If it possible to check if the type of image if it was renamed from .png to .jpg ?

I need this because when I use a resize function my website stop working if the uploaded image was renamed from .png to .jpg (I made my code to accept only .jpg images)

Answer 1

Every .png starts with these bytes:

89 50 4E 47 0D 0A 1A 0A

They are the PNG signature. If a .jpg starts with those bytes, it is not a jpg.

Answer 2

getimagesize will contain info about image type:

$info = getimagesize('file.png');
if($info[2] == IMAGETYPE_JPEG){

}

Answer 3

You can always read the image type to check an image using exif_imagetype()

$image_type = exif_imagetype($filename);

Example:

<?php
if (exif_imagetype('image.gif') != IMAGETYPE_GIF) {
    echo 'The picture is not a gif';
}
?>

Answer 4

Yes you can use this

if($_FILES["imagefile"]["type"] == "image/jpeg")
{

return true;

}

else if($_FILES["imagefile"]["type"] == "image/png")

{

return false;

}

Or you should use this mime_content_type is more reliable because the $_FILES["imagefile"]["type"] can be faked from client side...

Answer 5

What you need to know is not the history of the file, but its real format. You can do that by examining the file's content: JPG files should begin with the bytes FF D8 and end with FF D9. PNG files start with a different signature: \\211 PNG \\r \\n \\032 \\n (in hexadecimal: 89 50 4E 47 0D 0A 1A 0A).

See this website for more information: http://en.wikipedia.org/wiki/Magic_number_%28programming%29

Answer 6

Try the file command.

When unknownimage is a JPG image:

$ file unknownimage 
unknownimage: JPEG image data, baseline, precision 8, 400x400, frames 3

When unknownimage file is a PNG image:

$ file unknownimage 
unknownimage: PNG image data, 779 x 701, 8-bit/color RGBA, non-interlaced