Save photos from computer directly into camera roll or similar?

No easy solution for that one. Dropbox or Google Drive or the like as you mentioned, likely one at a time, emailing them to yourself, even worse, or perhaps putting them on a flash drive and finding a friend with a Mac. You could then AirDrop them - a little faster but still time consuming for 1,000 pics. You could also try Lenovo's App, SHAREit. It works on iOS and PCs as well, maybe a bit better but not as good as Airdrop. Otherwise you are stuck with the iTunes sync. In the future I suggest importing the photos instead of copy and paste. Import photos and videos from your iPhone, iPad, or iPod touch - Apple Support

Have you tried looking in your Recently Deleted album on the iPhone? If you see them there, you can "Recover All".

Cheers,

GB

Hmm, I have an iPad so does syncing the photos there and then air dropping them onto my phone sound relatively reasonable? I might give that a try

Well, yes and no. Yes you can sync them to the iPad fairly quickly over USB through iTunes. No (or maybe a yes), you can use AirDrop from the iPad ot the iPhone and end up with your photos in Camera Roll but it will take you a long time to AD 1,000 photos.

Give me a minute, I am going to test something and I will be back...

Ok, I am back. Try this with a dozen pictures to see if it works for you.

Sync a dozen or so to the iPhone, not the iPad. Then on the synced album, click on Select, Select All, then click on the box with the up arrow on the lower left, then Duplicate. This will put a copy on Camera Roll. You may then be able to do a new sync with no photos selected to delete the album that was synced while perhaps retaining the copies in Camera Roll. Try it with a dozen before you do 1,000.

It may work. I tried it and it does work up to the point of doing a resync with nothing selected. I did not want to proceed to that step but I suspect it will let you resync and thus delete the synced album. The only doubt I have is whether the "copies" are actual copies or pointers. I am guessing copies but you will soon find out... good luck.

My pleasure. Glad to hear.