Fabricate, but only if you can make the Craft check
Fabricate will turn paper and paint into a painting in 1 round (unless it’s a really big painting), but it still depends on your skills. Presumably, having something to copy from should reduce the DC, but the rules don’t describe this in any kind of detail.
Fabricate is a 5th-level Sor/Wiz spell, which probably qualifies as “high-level,” though. However, psionic fabricate is also a 4th-level power for shaper psions and ardents with the Creation Mantle; that might help, possibly.
Guidance of the avatar can help with the check
Guidance of the avatar is a 2nd-level cleric spell that grants a +20 bonus on one skill check. You can have a cleric cast it on you, which is convenient since it saves the artist from having to be a cleric with the Artifice or Greed domains (the only ones that get fabricate).
Therefore, if 9th level isn’t too high, and a 7th-level (for the spell slots) cleric assistant isn’t too much to ask for, you’re looking at 10 copies per day. Which still seems kind of ridiculous, and that set-up (guidance of the avatar plus fabricate) could generate something much more impressive.
You can get items of these
A dorje of a 4th-level power like psionic fabricate costs 21,000 gp. A wand of guidance of the avatar costs 4,500 gp. So 25,500 gp for 50 paintings, or 510 gp per painting. A single level of shaper psion or ardent with Creation and a single level of sorcerer, wizard, or cleric with Artifice, Magic, or Greed allows both to be activated without having to make any kind of skill check.
Alternatively, a 1st-level shaper psion or Creation ardent can take ranks in Use Magic Device (either cross-class, or in-class for the ardent using the Magic mantle). The DC to activate any wand is 20, and the use of guidance of the avatar isn’t exactly time-sensitive, so you can just keep attempting to activate it until you get it. If you roll a natural-1 while trying, you are locked out for the rest of the day, but a bonus on the check between +4 and +10 should be pretty easy, so you will most likely get it before you roll a 1. And then the Magic Device Attunement feat from Complete Mage allows you to attune to the wand, so you don’t need another UMD check for the rest of the day.
The opposite is also conceivable: a 1st-level cleric with the Artifice, Magic, or Greed domains can activate a wand of guidance of the avatar as well as a spell-trigger item of fabricate with no checks. The problem is that fabricate is a 5th-level spell, and wands are limited to 4th-level spells. However, a scepter of fabricate is possible: scepters from Lost Empires of Faerûn are spell-trigger devices, like wands, but can contain higher-level spells. The scepter of fabricate would cost 33,750 gp though, raising our cost per painting to 765 gp.
With this combo, burning through all 50 charges on both dorje-or-scepter and wand takes about 10 minutes, and produces 50 paintings. Again, though, the same set up could produce 50 copies of something much more significant than a painting.
Amanuensis doesn’t help, but could provide precendent
Amanuensis is a cantrip from Spell Compendium that rapidly duplicates nonmagical written words. It explicitly cannot copy illustrations or magical text. But it is also just a cantrip: if a cantrip cast as a standard action can be left unattended to copy up to 2,500 words per caster level, flipping pages as necessary, it seems eminently reasonable to have higher-level versions that can do more.
Simply copying a single illustration as a standard action thus seems reasonable as a 1st-level spell, if not a separate cantrip that does just that. An automated painting-copier spell, along the lines of amanuensis, that copies say a square foot of painting per minute and lasts 10 minutes per level, as amanuensis does, starting a new copy each time it completes one, is at best 2nd- or 3rd-level magic.