The getIteratorIndex function of the ImageMagick function works on any type of image, but it is built for measuring the number of frames in an animated .gif file. For non-animated image files, like regular .bmp or .jpg files, this function will always return the number '0', meaning that there is only one frame. Counting starts from zero with this function, so a .gif file with five different frames will return a value of '4' on this. Highly repetitive, but psychedelic animated GIF's are often anywhere between 10 and 30 frames, but a .gif file that is nothing more than video footage converted to a datafile may have hundreds of frames.
According to Wikipedia (in the article for "Graphics Interchange Format"), an animated GIf image is a uses the GIF standard "which allows various images (frames) in the file to be painted with time delays." This function won't get you the amount of time that delays between each frame, but it will give you the number of unique frames in a .gif file. This will tell you how complicated or simple the animation may be.
Is the 'getIteratorIndex' function not working for you? Try the 'getImageIndex' function, which produces the same exact result.
Some sample code :
$imagick_type = new Imagick();
$file_to_grab = "image_workshop_directory/test.gif";
$file_handle_for_viewing_image_file = fopen($file_to_grab, 'a+');
$image_iterator_index = $imagick_type->getIteratorIndex();
print("Number of Unique Frames in the .GIF File: $image_iterator_index");