ab12345678abcd Unfortunately, I think the second method proposed by Spinebot is not realistic.
The solution Spinebot first suggested—separating images you want packed in JPG format from those you want packed in PNG format into different folders and placing a pack.json file in each—is a practical approach.
You're not limited to using just one pack.json file. You can place one in each folder. For example, if you want to exclude certain images from packing, group them under a folder and place a pack.json file containing the following text in that folder:
{
ignore: true
}
This will ensure all image files within that folder are excluded from packing.