How do I develop a healthier relationship with images?

I have realised that visual images are a very complex category, both in genre and subject. I feel like this is the last part of my old life that I need to put in check, but I have been trying on and off for 2 months now in quarantine.

If by "put in check" you mean controlling your view of yourself in the past, then that may be a form of unwholesome clinging (attavadupadana). From a buddhist perspective this may create suffering based on the false assumptions (vipallasa) of:

• the notion that these photos and their representation of the views you wish to sustain are necessary for your wellbeing, and conversely

• the notion that getting rid of them would cause you emotional harm.

  "These four, O Monks, are distortions of perception, distortions of thought distortions of view...

  Sensing no change in the changing, Sensing pleasure in suffering, Assuming "self" where there's no self, Sensing the un-lovely as lovely"

https://www.accesstoinsight.org/tipitaka/an/an04/an04.049.olen.html

How do I make sure that I am only saving things that will help my spiritual practice and how do I get rid of unhelpful or unnecessary images that perhaps look nice or so on?

To put it blunt, the quick and dirty answer is that saving things like photos will not help your spiritual practice at all. As an ideal, all tendencies of upadana should cease as quickly as possible (nekkhamma).

To nuance things a bit, i think it would be more compassionate to acknowledge that upadana (clinging) has a particular emotional meaning and that one is allowed some time to process the renunciation of said clinging. It would be cruel - however effective it may be - to instantly jettison all and every attachment we might have, and i doubt it would be beneficial for one's practice to push forward in such brutal manner. Nevertheless renunciation is the recommended way to establish middle way equanimity (upeksha).

The introspection re the items is good: maybe don't need to do Anything with them; might even be occasionally useful for reference etc. As long as the machine space isn't needed for something else, then seems ok. Actually clinging to whether its ok or isnt might be fettersome. And if they dont matter so much, then they dont matter so much. Leaving them there seems relatively ok. Maybe its a good example of actual nonattachment: isnt necessary to declare an illusion is gone, and that in fact might imply some clinging was still there! In a few dozen centuries they'll probably be gone anyway, and if they aren't gone, finding them might make some archaeologist very happy! And it doesn't as though they're awful or anything. An to an extent, neatness is in the 'mind', and removing things rather than simply disregarding them to some extent might make for more clingyness. So maybe there's no rush to erase them. And maybe look through a couple introductory texts re The Middle Way, & The Four Noble Truths, & The Noble Eightfold Path, as they may tell useful detail re those things! Interesting question.

Just drop it all and move on. Never hesitate to let go of old stuff that has done its job. Don't be nostalgic, don't regret - that is petty thinking. You had it, you got it, you done it - drop it and walk into your next life.

It may seem like it's important and it was at some point, but you'll make plenty of new and more important stuff as you go forward. It's "you-the-emptiness" is what really matters, "you-the-fresh-look", "you-the-not-knowing". You have basic sanity - which means you don't have to carry anything along. Wherever you go you will create everything anew, from scratch, and meet everything you need to meet, there will be a plenty.

Have no fear. Drop and let go.