Can the mother of a friend of mine practice sorcery on me or my friends using my picture, even though I know I put my trust in Allah and consistently observe remembrances (dhikr) and prayers?

There is no knowledge concerning the extent of a sorcerer's power, but there is no need to worry. Cling to Allah and rely on Him, for benefit and harm are in the hand of Allah alone. Adhere to His obedience and avoid disobeying Him. Increase your recitation of the Quran and remembrance of Allah, and regularly observe the morning and evening adhkar, especially Surat Al-Baqarah, the Mu'awwidhatain (Surahs Al-Falaq and An-Nas), and the supplication "In the name of Allah, with Whose name nothing whatsoever on earth or in heaven can inflict harm..." Supplicate to Allah and seek refuge in Him, for He is the best preserver.