Hi Horst, thank you for your warm welcome
My question indeed needed a little more details. I'm using processwire as an API for a backbone webapp. (artexis-app, best to view it in chrome )
I'm also port it to an Ipad application with Apache Cordova.
It has to work offline, so I download all the assets to the Ipad. I included an update function and it checks the file name, I want to add a timestamp the the cropped image to see if it has changed. Like: image_1447076736.-thumbnail.jpg.
I can't use the modified property of the image, because that's changed when it's downloaded on the Ipad.
@Adrian:
Thanks for your suggestion, but I think that only applies when the image is uploaded and not the cropped image. Is that correct?