Here is the full list of all 34 Pixel Puzzles Mosaics achievements. It takes around 5-6 hours to unlock all of the achievements on Windows.
Complete Mosaic:
Complete Mosaic: Nebula
Complete Mosaic: Sun Flowers
Complete Mosaic: Crab
Complete Mosaic: Fish
Complete Mosaic: Canario
Complete Mosaic: Route 66
Complete Mosaic: Mural
Complete Mosaic: Bacteria
Complete Mosaic: Forest Fire
Complete Mosaic: Dragon
Complete Mosaic: Flowers
Complete Mosaic: Waterfall
Complete Mosaic: Books
Complete Mosaic: Wagon
Complete Mosaic: Burger
Complete Mosaic: Urban Decay
Complete Mosaic: Roulette
Complete Mosaic: Conkers
Complete Mosaic: Pasta
Complete Mosaic: Orca
Complete Mosaic: Tiger
Complete Mosaic: Gas Mask
Complete Mosaic: Sword
Complete Mosaic: Rose
Complete Mosaic: Cabin
Complete Mosaic: Pebbles