Upload the icon as /dbtech/thanks/images/<varname>.png where <varname> is the varname you chose for the button, like "thanks", "likes", "dislikes", "lols" etc.
Perfect!!! Can I use any size for the image? For example, I need to create a big button that users have to click on to see text of the post and partecipate to a contest.
Because we use the same style as the postfoot (i.e. the bit with the Blog this post etc buttons) it's really not designed to work with buttons bigger than the Thanks, Like and Dislike buttons.
You could try, but any undesired look / behaviour is not something we're able to give support for at this point in time
We plan to allow further customisation options in a future version