a few words about web development

How to check if image was upscaled

Detecting low-quality images programatiacally
$url = 'http://your_server.com/image.png';
$data = json_decode(file_get_contents('http://api.rest7.com/v1/image_upscaled.php?url=' . $url));

if (@$data->success !== 1)
if ($data->is_upscaled) 
    echo 'The image was upscaled. It was originally ' . $data->original_width . 'x' . $data->original_height;

So how does this work?
Let's say we have this image, 300x200:

Now we upscale it to 600x400 using Lanczos:
and we send this image to the API using our script above. The API returns this array, in JSON:
  "is_upscaled": true,
  "current_width": "600",
  "current_height": "400",
  "original_width": 300,
  "original_height": 200,
  "accuracy": "68%",
  "accuracy_width": "67%",
  "accuracy_height": "69%",
  "cropped": "",
  "success": 1
Then this array is parsed by our script and it prints:
The image was upscaled. It was originally 300x200