Uncaught Error: Call to a member function toHex()

```
include('vendor/autoload.php');

use Jenssegers\ImageHash\ImageHash;
use Jenssegers\ImageHash\Implementations\DifferenceHash;

$hasher = new ImageHash(new DifferenceHash());
$hash = $hasher->hash('img/forest-copyright.jpg');

echo $hash->toHex();` <----- Fatal error: Uncaught Error: Call to a member function toHex() on string ...
```
Why?

Reproduce the provided PHP snippet using ImageHash and DifferenceHash, then inspect the return value from ImageHash::hash before the toHex() call. Check the project’s API documentation or tests for the expected hash type; done means the cause and correct usage are clarified or covered by a regression test.

Written by the indexing model from the issue text.