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