how do I add some files from an external iOS device to my time machine disc?

I want to add some photos from a macbook

Just to clarify: you are looking to add something from your Macbook (in your post) or an iOS device (in your subject line) to your Mac?

If it's your Macbook and only a couple of photos, how about copying them to a thumb drive and then copying them from there to whatever machine you are backing up with Time Machine.