It depends upon the forum supported software. Some have a dedicated mobile device support, which would then allow you to upload photos directly. Otherwise, you can always upload them to a hosting site and then link to them in your Orchid Board postings. I have to believe some of the more popular photo hosting websites have mobile phone support these days.
This forum supports the taptalk app - unfortunately, its use is temporarily suspended. Once Marty turns t back on, you can post pics from an iPhone with ease (without having to use a 3rd party site).