How to load large images (the paths to them are included in the array) in the background with a progress bar displaying by the size of the images (indication: how many have already been downloaded to the total file size)?
Everything that I found is related to input-file and ajax, in which the total file size is taken and how much has already been downloaded.
Everything is correct. Image provides the ability to obtain information only about the success of the download, but not about its process. Therefore, the option with XMLHttpRequest seems to be the easiest way to solve your problem.