It is not permissible
to keep the photos taken as mementos, but they should be wiped out, for the Prophet (peace be upon him) said to
`Aly (may Allah be pleased with him):
Spare no portrait unwiped out, and leave not a high grave unleveled.
(Related by Imam
Muslim in his Sahih 'authentic' Book of Hadith).
As for the pictures found in a book, a magazine, or a newspaper which you need (Part No. 1; Page No. 702) to keep, you could just wipe out and deform them.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.