We've actually had members of parliament in the Netherlands proudly show of the selfies they took in the ballot booth with their ballot on Twitter, encouraging people to take selfies (nicknamed 'stemfies'; a portmanteau of vote ('stem') and selfie) to show that (and how!) you voted on social media.

The election council and a lot of privacy-conscious citizens weren't amused to say the least, but a subsequent ruling by a judge turned out that it isn't strictly speaking illegal, because the law doesn't explicitly prohibit photography in the ballot booth. So until parliament enacts a law that forbids it (like Germany), we are stuck with this rather dubious phenomenon.

At least we've banned voting computers for a good while — the ones we had ran closed source software and the votes cast couldn't be verified by the voters or the election council — so there's that.

It depends on your definition (there is no fine or anything) but it's now explicitly prohibited and poll workers are required to reject such voters (and give them a new ballot), see § 56 Abs. 2, 6 Nr. 5a BWO.