I've found another solution that works pretty well.
I put photos that I would like to post to the boards up on an account at Google Photos
. The service is free, easy to use, virtually unlimited, and has some nice organization features built in. Whether or not you trust Google with your photos is a separate issue.
When I post a single image to the board, I don't necessarily want to inadvertently give viewers the capacity to browse my whole gallery (you can do this if you want to, but let's assume you don't for now). The solution is to select the single photo you would like to post within Google's gallery, and then "right click" on the expanded view of that image to select the option "Copy Image Address". This will give you a link to just the single photo, without an implied invitation to browse the entire collection.
The last issue is actually getting that image to show up in Axiom's board software. First, click the "Enter an Image" icon (in the "Full Reply Screen", etc. context). Then, post the link you copied from Google Photos into the pop-up text box. BUT ... if you leave it like this the Axiom software WON'T recognize it as an image and won't post it, since it doesn't recognize the address as pointing to a known image format. We can fix this easily. Here's the trick: A "?" (question mark) at the end of a web address is ignored, and following text is interpreted as "query string" meta data (key/value pairs for a form, etc). So, if we add a "?" to the end of the web address, anything after that will not alter the location to where it points. But, the boards want an image formatting tag, like JPEG, or etc. as the last item in the address. So, all together, we will just type "?.jpg" into the text box right after the pasted URL from Google, and voila ... everything works great! The Axiom boards now recognize the link as an image, and will correctly embed it, but the real URL has only had a meaningless comment appended, and still points to the same location on the web.
I recommend using the "non-floating" option in the pop-up image entry field. Otherwise, the image will tend to be shown at full size, and surrounding text will be very hard to read (very long text lines). If a viewer wants to see the full-size image, they can right-click to "open image in new tab", etc. If you want to get fancy, you can embed the image code inside a link, and then automate the usual "click to expand" functionality. However, this seems to have the effect of showing the image as full size in the post itself, which defeats the purpose. If you really want to work around the issue, I suppose that you could have two image sizes stored, linking to the larger, and embedding the smaller.