Show HN: My startup PrintMosaic runs a contest for the first time. Any advice?

Hello, I've been running PrintMosaic for a while (https://www.printmosaic.com) and I am now experimenting with contests.

PrintMosaic allows people to create photo mosaics easily. Choose your main image then choose the small images and it assembles them for you. It is then possible to order a print or a high resolution image if you want to print yourself.

The current contest allows people to win a free poster as well as credits for high resolution images.

In order to enter the contest, all you need to do is to create your mosaic and apply with it. The mosaic with the most votes wins. So you might need to invite your friends to vote for your mosaic. This contest ends on November 30, so the votes will be counted at midnight that day.

Here is the contest page, with rules and prizes: https://www.printmosaic.com/contest/events/1-November

Is there anyone here who has run a similar type of contest on their startup? I would be curious to hear stories. I'll be happy to share my experience once this is done as well.