I had the change to see some of them in the British museum and in the Louvre. They make part of my favourite roman artwork list, how could be not possible?! I noticed that some people here used them as avatars, like Artemisia Papirus and the old Porciae avatar.
They are called El Fayum Mummies because most of them were found in that disctric in Egypt (Hawara, er-Rubayat), even if other sites gave also a great number of portraits, like Menfis or Tebas. Looking at them, we witness a beautiful symbiosis of greco-roman painting style and egyptian funeral portraits.