Here's a zero word answer to the question ... why do you think you need to make specific mention of which bunch of pictures you are referring to? If I received a letter with pictures pasted into it, printed into it, stapled to it, or simply included in the same envelope, then a sentence, in the letter, such as
Have a look at the pictures, some of the ones I took on my last trip to Shangri-la
isn't going to have me wondering which pictures I should be looking for or at. If you want to call attention to particular pictures you might want to scribble numbers on them so you can write
Picture 6 is the young woman I spent a lot of time with in Shangri-la
to avoid confusion with the pictures of your sister.
I see no need for attached or pasted or included