How can I check whether or not a file is an image?

Question

Can I check whether or not a certain file is an image? How can do this in PHP?

If the file is not an image, I want to give an alert message.

Answer 1

in PHP you can do it like following way

if ((($_FILES['profile_picture']['type'] == 'image/gif') || ($_FILES['profile_picture']['type'] == 'image/jpeg') || ($_FILES['profile_picture']['type'] == 'image/png')))

in Javascript You can do it like following way

function checkFile() {
   var filename = document.getElementById("upload_file").value;
   var ext = getExt(filename);
 //  alert(filename.files[0].filesize);
  // alert(ext);
   if(ext == "gif" || ext == "jpg" || ext=="png")
      return true;
   alert("Please upload .gif, .jpg and .png files only.");
   document.getElementById("upload_file").value='';
   return false;
}

function getExt(filename) {
   var dot_pos = filename.lastIndexOf(".");
   if(dot_pos == -1)
      return "";
   return filename.substr(dot_pos+1).toLowerCase();
}

Answer 2

In addition to getimagesize(), you can use exif_imagetype()

exif_imagetype() reads the first bytes of an image and checks its signature.

When a correct signature is found, the appropriate constant value will be returned otherwise the return value is FALSE. The return value is the same value that getimagesize() returns in index 2 but exif_imagetype() is much faster.

For both functions, FALSE is returned if the file is not determined to be an image.