I've now tried the Phoca Open Graph Plugin together with Phoca Gallery Plugin, and it doesn't find the article image produced by phocagallery plugin code. I've set the plugin order so that the open graph plugin should be running after the gallery plugin. Also I've set open graph plugin options -> Common Options -> Image (Parameter) Order to Last.
In "Setting of images in open graph", point 5), you state:
Please also expand plugin code during the in-article image search in 5). If that would be easier, please at least expand your own gallery plugin's code to an image specially.5) If no image is set in plugin parameters or article parameters, Phoca Open Graph plugin tries to find an image inside the article. If some is found, such will be used in og:image meta tag.
The reason I'm interested in this is that the site owner shall be able to upload images (this works! using your gallery) and create articles from them (which uses your button plugin and, after that, your gallery plugin; this workflow seems to be slightly too complicated already). The same image shall then appear when sharing on Facebook. If you say it's impossible or otherwise wontfix, I could *possibly* teach the site owner to manually set the mid-size preview image generated by your gallery as article intro image manually, but that would lose the ability to click on it in the blog view and get the enlarged view and then switch through all phocagallery-plugin-generated images on the blog view by simple further clicks inside the image. (I don't know whether this is an explicit feature or rather an accident with the options used here, but this is quite nice.)
Regards,
Fabian