General advises
  

It is not very easy to make good looking mosaic.

If you couldn't do it the first time, try to determine why.

Maybe  you do not have enough image tiles.

Try  and find more. If you don't have more photos available - you may try to use your existed photos "more creative".
See here for hints.

Maybe  the source picture you want to make as a mosaic has too many small details.
For example - It is hard to make mosaic from a group photo.

Try  to cut, crop or modify your source picture to leave only an easily recognizable object, like face of man or head of dog.

Maybe  the colors pictures you are using as a tile don't have enough common colors with the pictures you want to render.
For example: It is hard to make brown sun tanned face out of pictures of light blue snow mountains. (Even if you have more than enough pictures of those mountains). In this case - try to correct the color of face.

Try to  make it more pale, more contrast, or something else.

  
 
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