I predominantly take and post pics with my iPad, sometimes with my iPhone.
When it's time to post:
> I compose the message
> scroll (push up screen) to "Choose file" (beneath blue Post a Follow-Up)
> select from camera roll OR Album (each of my hosta has it's own album)
> select a photo
> your photo will appear beside "choose file"
> select "Preview Message"
>>> your message will appear including your photo.
>>> if satisfactory! select "Submit" and you are done!

Should you need to change photo, simply select "choose photo" again and repeat process. The last photo supersedes previous photos.

Once you have selected the photo, then, say you decide to add or amend your comments, you will have to re-choose your photo again. It does not hold. Choosing your photo should be the last function you perform before previewing your message.

I hope I haven't forgotten anything. Let us know if it works - over 300 hostas you say? Wow - we're ready for pics! We love pics!

wELCOME to the forum! Glad to have you! :-)

Jo