This problem has been an issue ever since Apple changed IOS from iPhoto to Photos back in 2014 and again since they did the same to Yosemite this year. Even their own Mail app does not recognize that photo's are stored in Photos. My issues are more severe than that, I can always find a photo and copy it to a mail message, but when you're trying to design a webpage that only recognizes iPhoto, that is a different matter. I have been beating my head against a wall to find a solution since I cannot copy and drop a whole folder of pictures for a Flash presentation into a webpage design, it just doesn't work that way. Apple does these little software design changes that really serve no purpose other than change the name of a program. Photos does nothing more than what iPhoto did before, in fact, it is a clumsy change to say the least, especially since other programs don't recognize it, including Apple's own Mail.
The other IOS issue was that Blogger, a Google application for blogging on line, also didn't work when Apple changed the iPhoto/Photos application design. I was over in Europe in the middle of a travel blog and found out I didn't have access to my photo's which were absolutely critical to my work. If I wasn't in the middle of the Vatican I would of said a few choice words.
Now, as far as your issue of inserting photo's into your documents. If it is only a few photo's, and not a whole slideshow, I would put it on your desktop, by dragging it from Photos, and then attaching it to your document or mail document from there. I'm sure that MSW will not recognize Photos nor will your mailer. Welcome to Apple.