It looks like imgur has an
api, but it doesn't look like the API can retrieve images currently. Perhaps they may be willing to add such functionality.
If they add it as a paid feature, I don't think the forum should go down that road. It would set a precendent for other image hosts to do the same.
I disagree. Imgur is providing a service (hosting images), and deserves to earn a fair profit. It would cost money for the forum to host images on its own infrastructure, and as long as the cost to use imgur (and all other image hosting sites) is less than the cost of self-hosting, it will make sense to pay.
I presume that imgur usually makes its money from ads when people access images on its imgur site (not the raw image that is accessed via the forum image proxy). I presume that the image proxy complicates various metrics that imgur uses.