I found the solution just today. First you install pic2cam from play store. Then you enable the audio/video notes plugin in osmand. Then any place you want to add photos to you can tap on that place>then actions>then take photo> then select pic2cam from the camera apps, you can select any photo from gallery.
Osmand doesn’t allow you to select photos but only capture them, however pic2cam tricks the phone so that phone considers pic2cam as a camera app.