Paint it Back's achievements are very simple. The game's 20 achievements can be broken down as follows:

• 4 gallery (completion) achievements
  
• 5 difficulty achievements
  
• 4 Mystery Masterpiece (quick fix) achievements
  
• 7 Mystery Masterpiece (glory) achievements

All achievement progress can be tracked via the in-game menu.

All of the game's puzzles are divided into galleries, each with its own theme. Finishing every puzzle in all but one gallery is required for all the achievements. Completing a puzzle awards 1-3 ribbons (depending on difficulty played).

Galleries:

1. Training Hall
   
2. Portraits
   
3. The Nature of Things
   
4. Having a Bad Day
   
5. Good Advice
   
6. Big Time Bugs
   
7. Animal Dilemmas
   
8. Scenes From Dreams
   
9. Home Sweet Home
   
10. Forgeries
    
11. Curiosities
    
12. Portraits II
    
13. Sports of Sorts
    
14. The Archives
    
15. 2016 US Election

The first 13 galleries total 300 ribbons.
The Archives adds 29 more and 2016 US Election adds 30, totalling 359 ribbons in the game.

• Completing Training Hall unlocks 🏆 Told You I'm an Artist - Demonstrate some artistic ability.
  
• Completing enough puzzles to receive 100 ribbons unlocks 🏆 Logic Master - Win 100 ribbons.
  
• Completing Galleries 2-13 unlocks 🏆 Surreal Superhero - Reopen the whole gallery.
  
• Completing The Archives unlocks 🏆 Basement Dweller - Repaint all of The Archives.
  
• Completing 2016 US Election doesn't unlock anything achievement-wise.

Most puzzles can be played in multiple difficulties: Normal, Pro, and Master. The final result is the same, but the large puzzles are split into multiple smaller sections when played on the lower difficulties.

The difficulty affects the number of ribbons you receive. To quote the developer:

Originally posted by CasualLabs:

So - you can win a max of three ribbons from a big painting.
If you solve it on Normal, you get one ribbon.
If you solve it on Pro, you get two ribbons.
If you solve it on Master, you get three ribbons.
If you've beaten it on Master, re-solving it won't win you any new ribbons.

🏆 Exhibitionist - Paint 20 Normal pictures
🏆 Extremely Normal - Paint 50 Normal pictures
🏆 Budding Professional - Paint 5 Pro pictures
🏆 Hardcore Professional - Paint 20 Pro pictures
🏆 Master Master - Paint 25 Master pictures

• If you complete every puzzle on the highest difficulty for the maximum number of ribbons, you will only complete 43 normal pictures. You will need to go back and redo 7 pro/master puzzles on normal for Extremely Normal.
  
• If you aren't interested in collecting all the ribbons (there's no achievement for it), after unlocking the three pro/master achievements, it should be fine to complete the rest of the game's puzzles on normal.

Mudslide has posted solutions for the Master pictures if needed:
https://steamproxy-script.pipiskins.com/sharedfiles/filedetails/?id=607819719

Mystery Masterpiece is separated into two modes: Quick Fix and Glory.
Both are the same in that a puzzle is selected at random from one of the other galleries. Other than that, there's virtually no difference to solving the puzzles normally.


Quick Fix mode choose smaller normal/pro-sized puzzles, from 5x5 to 12x12. There are 4 achievements:
🏆 One Track Finger - Paint 1 Quick Fix pic without lifting your brush
🏆 Continuous Madness - Paint 5 Quick Fix pics without lifting your brush
🏆 X Marks the Weenies - Paint 5 Quick Fix pics using no X's
🏆 I Can Do this Blindfolded - Paint 20 Quick Fix pics using no X's

• Without lifting your brush means not letting go of the mouse button once the first square is coloured until the puzzle is solved. Mistake can't be made as erasing squares requires letting go of the mouse button. Moving the cursor outside the drawing area is fine.
  
• No X's simply means solving the puzzle without X's. Not too difficult on the smaller puzzles.
  
• You can quit/re-enter for a new puzzle and only play the smaller ones for an easier time.

Glory mode has a difficulty selection but all the puzzles are pro/master-sized. Playing on normal will divide the puzzle into smaller sections, similar to the main game. Completing a puzzle in Glory mode awards you with up to 4 types of ribbons unique to this mode:

• Checkmark Ribbon: Complete the puzzle. 1-3 are awarded based on difficulty selected.
  
• Timer Ribbon: Complete the puzzle within the alloted time.
  
• Paint Ribbon: Complete the puzzle erasing less than a number of squares (i.e. mistakes).
  
• No-X's ribbon: Complete the puzzle using less than a number of X's.

There are seven achievements, all for collecting these ribbons:
🏆 Minor Mix-Up - Win 5 checkmark ribbons
🏆 Major Mix-Up - Win 25 checkmark ribbons
🏆 Picking Up Speed - Win 3 timer ribbons
🏆 Fast and Pretty - Win 15 timer ribbons
🏆 Attention for Retention - Win 3 paint ribbons
🏆 Practical Painter - Win 15 paint ribbons
🏆 Painted from Memory - Win 10 no-X's ribbons

• It's obviously easiest to play normal difficulty. Completing master puzzles with a limit on the X's is quite difficult.
  
• Like Quick Fix, you can quit/re-enter for easier puzzles.