Update - by using side-by-side apps in iOS 11, i can copy the photo and paste into EN. Ideally, it would be great to drag the photo into the note, but this removes the back and forth of seeing photo, going to EN and adding it from there.
I think what they're asking for is a way to send a photo from Camera Roll to an existing Evernote note on the phone. You can send a photo to a new note, but i don't see a way to send a photo to an existing note. Apple Notes has this feature which is helpful when you're adding photos to your existing notes. When you have hundreds of photos, it's easier to view them in Camera Roll, then send them to notes, rather than starting in the existing note and trying to find the photo you wish to add.