ios merge two imageviews like 'words with friends' scrabble game board

ios merge two imageviews like 'words with friends' scrabble game board

please improve my learning by telling me that how can i achieved like
attached game board , when user drag the tile from tile bag to board and
after that when he click on play it merge all the tiles and make it one,i
did lot Google but didn't get optimized solution . Please help me.