My personal experience was there wasn't much software for truly manipulating photos on PCs or anything else a average non pro would have access too before photoshop.
Everything I'm aware of before photoshop in the PC space was basically a pixel editor. It might have had brushes like Deluxe Paint. It might have supported 24 bit images maybe possibly. But it didn't have any things I thought of as "photo" manipulation like adjusting hues, values, curves, blurring, burning, dodging, smudging, etc. etc. They just let you draw solid colors shapes, possibly gradients, and cut and paste, maybe rotate, scale, and warp.
The problem was that stock Amigas and older PCs didn't have true colour, they mostly had index-colour modes where each pixel was a lookup into a table of usually up to 256 colours, rather than a direct RGB value.
Doing photo manipulation operations would have been difficult unless you did everything on a logical 24bit document and constantly resampled and dithered down to an indexed screen mode. I don't know if anyone tried this, but I imagine it would have been slow and hard to work with.
The Amiga had HAM and later, HAM8 which allowed 4096 and 262000 colours respectively, but they were cumbersome for editing; they were more a means of displaying renders or scanned images than anything else.
I remember the Amiga having 3 tiers of graphics program. You had pixel editors like DPaint, Photon Paint, or Brilliance, then you had image processing programs like ADPro (Art Department Professional) and ImageFX. These programs could perform convolution filters, image composition etc. And with 24-bit output. But they did so in a almost batch-program-like manner[1]. You couldn't paint or play around with things like in Photoshop.
At the very top of the tree you had programs like TV-Paint and ToasterPaint which ran on high-end Amigas with expensive 24bit colour boards. I only ever read about these programs, they were inaccessible to a teenage hacker. While they let you edit images in 24bit colour, they were geared more to video and broadcast graphics. They were closer in spirit to the Quantel Paintbox or Symbolics S-Graphics than the print-oriented Photoshop.
Towards the end of the Amiga's life there was Photogenics, which was probably the closest thing to Photoshop, but by this time Amiga devs were consciously playing catch-up with the PC and Mac and the users were moving on to other platforms.
[1] (edit) Here is a video of someone using ADPro.(https://www.youtube.com/watch?v=0Ef32uNqdIE) You can see that they use a text-ish interface to select a number of operations to be performed on an image. They then click "execute" and wait for the result to be rendered.
I'd be interested in seeing a history of early photo editing software. I remember editing photos in the 90's (I still have some print-outs of the results), but I have no recollection of what software I was using other than that it was not photoshop!
I remember it fondly as well. It was a lot cheaper but had remarkable capabilities. It kept getting more and more bloated though. I think version 9 was the last one that one could actually use.
My grandmother had a picture of her 4 children from the early 50s. Just faces, floating in diamond arrangement. I remember being greatly confused by that, unable to imagine compositing in those days.
Also, my father was into photography in the 70s, there were a few books about it in his desk. Last year I opened one. Every filter name I saw in 90s picture editing software was listed in it, in fact they were all photochemical process filters that were lifted in digital editors.
Interesting how your first link get displayed in fixed-width Asian-style characters here in Chromium, apparently because of the apostrophe (which itself is the only character displayed with a narrower width). Just removing the apostrophe in Chromium's address bar immediately makes all the text go back to a normal font. Firefox just shows "%C2%92".
Actually, it looks like what gets displayed as an apostrophe is just a control character, U+0092 <control> = PRIVATE USE TWO.
http://design.osu.edu/carlson/history/PDFs/paint.pdf
My personal experience was there wasn't much software for truly manipulating photos on PCs or anything else a average non pro would have access too before photoshop.
Everything I'm aware of before photoshop in the PC space was basically a pixel editor. It might have had brushes like Deluxe Paint. It might have supported 24 bit images maybe possibly. But it didn't have any things I thought of as "photo" manipulation like adjusting hues, values, curves, blurring, burning, dodging, smudging, etc. etc. They just let you draw solid colors shapes, possibly gradients, and cut and paste, maybe rotate, scale, and warp.