Progressive JPG is a image format, that contains low quality snapshots. These snapshots can be displayed during the transmission of the higher quality snapshot, which gives better end-user experience.
Progressive JPG is a image format, that can be progressively displayed in the web browser during its transmission.
Can end-user benefit form the progressive JPG, if the file is transferred over HTTPS? If the image is encrypted, snapshots would have to be separated...
Progressive JPG is a image format, that contains low quality snapshots
No, that’s not true¹. It is only one image – but saved in a way, that some ”broad”, lower-detail information is encoded first, and then more detailed data is coming later on, so that rendering can start early in lower quality, and as more details become available, the rendering can become more refined.
And serving such an image via HTTPS does not change that.
¹ Images can contain additional thumbnail version(s) inside the EXIF meta data – but that is not what the “progressive” format is about. And that feature is seldom used on the web, because it would increase the overall amount of data to be transferred (and I am not even sure if common browsers support this, in that they would display such a thumbnail first and then the full image once it is done loading.)