Answered by Sayyidi al-Ḥabīb `Umar bin Hafīẓ (may Allāh preserve him and benefit us by him).

What dhikr can be read to remove disturbing images from the mind?

Read regularly:

اللهُ مَعِيْ، اللهُ شَاهِدِيْ، اللهُ حَاضِرِيْ، اللهُ قَرِيْبٌ مِنِّيْ، اللهُ نَاظِرٌ إلَيَّ

Allāhu ma’ī, Allāhu shāhidī, Allāhu hāḍirī, Allāhu qarībun minnī, Allāh naẓirun ilayya

Allah is with me, Allah witnesses me, Allah is present with me, Allah is near me, Allah is watching me.

Read 100 times a day:

هُوَ اللهُ الَّذي لا إِلهَ إِلا هو عَالِمُ الغَيْبِ والشَّهادَةِ هُوَ الرَّحْمَنُ الرَّحِيم

Huw’Allāhu’lladhī lā ilāha illā hu, ‘Ālimu’l ghaybi wash-shahādah, Hu arrahmānu’ rahīm

He is Allāh, there is no god other than Him, knower of the unseen and the seen, He is the All-Compassionate, the All-Merciful. (Al-Ḥashr, 59:22)

Bestow abundant prayers upon the Prophet ﷺ. While doing so imagine that you are in the Blessed Rawḍah or in front of the Ka`bah. All of this will purify the heart and remove disturbing images.