Earlier quoted context omitted.
Really glad that you like it! I feel that it's a difficult site to monetize. Part of the appeal is that it can be more convenient than having a resizing application on your computer. I think adding sign in (a dependency for premium plans) would undermine that a bit. At the moment, it's still growing quickly, doesn't take up much of my time and costs barely anything to run. Given those circumstances, I don't feel I ne…
You may also consider using this tool to drive traffic to another product/service. It's advertising but you would benefit more than slapping on some Adwords. I think micropayment is a bad strategy, adding any payment/signup friction to a service like this and users are going to bounce
Drive traffic to something else: That's my current thinking.
Adwords: I think Adwords would make the site seem slower and ruin it a bit. I'd consider a single, short text snippet Amazon link, though. Eg. "Check out the latest Nikon DSLR on Amazon"
Micropayments I would only consider if a service emerged that was as simple as embedding a one-click button and took sufficient market share that it wouldn't be a barrier. I can see that the likelihood of this in the near future is small, though.