How can i make highlighter effect on the text/images using UI?

I am trying to get the highlighter effect as shown in the above image. its a kind of word search game and when the player drags its finger on the letters/word to find the required words. while dragging should generate a highlight effect on the word . i am using Unity UI. Any help would be appreciated Thanks!

Effect something like below using unity UI
link text

Simple use Button then you can adjust accordingly
BUtton propertyes