This will likely suffice for my purposes. (Although I'll have to create a variant which incorporates the retina-downsizing action you gave me a few days ago.)
I'll have to play with the second. It's not working properly even after I convert the filetype to .png, but obviously I now have a great foundation for the macro, so I'll just have to step through it methodically and work out why it's giving me an empty dialog box at the end.
Cheers