Is there an iPhone app for this?

[Ross]

I need an iPhone photo editing app that lets you crop and paste pictures into another one; can anyone help me?

[Daisy]

It looks like the collage function, with which you can assemble multiple photos into a single photo.
Well, I suggest Fotor to you. It's a photo editor online and it's also available on iPhone. I've been using it for a period and find it really a nice handy photo editor. Its photo effects are my favorite! After editing, I can directly save my photo on my computer or put my photo to facebook, flickr or twitter.
You can crop your photo first and then make a collage. There is a feature named free collage, maybe it will work with your purpose.

I think you should try their website first, then make a decision whether you should use their app.

Check it here:
http://www.fotor.com/
Check its collage feature here:
http://www.fotor.com/features/collage.html
Check its app here:
http://www.fotor.com/iphone/