Most of the thangkas are not aunthentic as the artist do not follow the proper iconography according to the Tibetan script. They are also unable to copy the individual letters in a size that is small in authentic ancient thangkas.
The close-up of the back of a fake thangka on the left shows a good example of this. For comparison, the correct spellings are added to the right of the counterfeiter's letters. Another indication of the forgery in this example was the size of the letters of 1.5 cm [not recognizable here because the correct syllables were inserted in the same size], which one never finds in this size on authentic scroll images. The forger has written the three syllables correctly, but the comparison with the correctly spelled syllables added to the right makes it clear that he did not master Tibetan caligraphy.
The example shows the most commonly used UCHEN font.
More about the different Tibetan scipts ...