Starting with the latest edition of Apple iOS 11, HEIC is your standard format for saving images on iDevices. Compared to JPEG, this format makes pictures smaller without sacrificing quality. The issue is that some users can't see the HEIC picture. The whole conversion process using heic.online https://heic.online/ takes place on your browser. The files that are downloaded are safe, and you may access them. After the conversion is completed, images will be deleted. So that you don't have to be concerned about your privacy.