Is there any online tool to convert the images to json file for annotation from image exceptionally made for ML app
There's quite a few third party tools for OD annotation. Here's a guide to getting the annotation in the right format, so as long as the tool you are using can export into this format, or convert to it, you should be okay.
https://developer.apple.com/documentation/createml/building-an-object-detector-data-source