Both of those mosaics were built in "Studs-Out" fashion (the bumps on the bricks face out toward the viewer).
The next most common way to build a mosaic is "Studs-Up" fashion where the bricks are stacked atop one another normally and the viewer is looking at the side of the bricks. Though you lose the squareness of the physical "pixels" when building studs-up, you gain resolution because the side of small LEGO plate pieces have a 2:5 height-to-length ratio.
I've build a few studs-up mosaics in the past (most notably a colorful tree frog and a giant grayscale portrait), but as this type of mosaic is a bit more laborious, for most commissions I steer clients toward the standard studs-out orientation.
My latest creation, however, is a studs-up mosaic, and it is yet a third rendition of the Mona Lisa. A woman in Australia asked if I could build one for her after seeing a version at LEGOLAND in Billund, Denmark. I told her that while I would not build an exact copy of someone else's mosaic work, I'd be happy to create a new version. After sending her preview images, she agreed, and within a few weeks I had ordered the pieces and completed the mosaic.
The rendition is quite good even though the size is much smaller than the studs-out mosaics mentioned above. This is partly due to the better resolution of style, but also because I cropped the image of the painting to focus more on the head of Mona Lisa. Here's a close-up of the face (the visible seam is there because the final mosaic was shipped in three smaller sections).
The mosaic used 10 different colors (Black, Dark Red, Orange, Tan, Light Gray, Gray, Dark Gray, Lime, Green, and Yellow). Well over 5,000 bricks and plates were included. It measured roughly 23" x 31" when complete.