Thank you Boštjan Gorenšek for reporting this.
I can validate this. The item is indeed saved but this notice is risen.

Thank you Boštjan Gorenšek for reporting this.
I can validate this. The item is indeed saved but this notice is risen.

Error message: The image was not uploaded. Please ensure that you used a valid image file and that file uploads are properly configured on your server.

Error log:
It looks like PHP's 'GD Image Library' is not installed/enabled on your system. Please ask your hosting company to enable/install it.
You'll need to enable cURL. That's a PHP extension that is enabled by default, but some hosts choose to disable it. You may need to contact your host to assist you in re-enabling it.

Mi host was upgrading php from 5.4 to 5.6
I Asked the host to install GD Image Library (PHP) and cURL.

Problem solved.

I hope that helps.

Thank you so much for reporting this Marcos :)