What is a quality beginners camera for photoshop use?
Any DSLR is suitable for Photoshop use.
Ok, couldn't resist.
But seriously, these days DSLRs have come a long way and it comes down to personal preference.
Nikon, Canon, Sony all make nice cameras.
Which company most people go with is usually dictated by the various lens offered by each company for their cameras.
I personally exclusively use Canon because I love their lenses and cameras.
I find the cameras more intuitive to use but that's just me.
Canon's lenses are also awesome but other companies also have fantastic lenses.
In the long run, once you build up a collection of lenses, you tend to or have to stick with that company.
Cameras come and go but your lenses stay with you for life, unless you're the type that always chases the most newest megapixel body.
Pick a company and stay with it, building up your lens collection.
If you pick Canon then any of the lower end entry level bodies are great, as with Nikon.
Don't just look at megapixel count, that's not what makes a great camera.
If you want a good starter camera look at Canon 750D or 760D, mid range camera look at Canon 70D.
These are all APS-C size sensors, meaning they are a smaller sensor than the old 35mm film size, this gives them a 1.6x crop factor so effectively you only get the inner portion of the image which makes the image look "bigger" than in a standard 35mm frame.
What is happening is it's just recording the inner part of the frame not the full 35mm frame that the old film used to record.
A fantastic full frame camera at the lower end of the market is the Canon 6D but I'm not sure of your budget.
Sorry I can't help with Nikon or Sony, my area of knowledge centres around Canon.
Hope that helps somewhat.
RB