http://swonderstzr43aczpcwdoyc25vwxngyromja7pyb5sf26ap3v535sxqd.onion/faq
HEIF stands for "High Efficiency Image Format", and, as the name
suggests, is a more streamlined way of storing image files. Using
advanced, modern compression methods it allows digital photographs to be
created in smaller files sizes, all while retaining higher image
quality than its JPEG alternative.