How to put about 50 pictures into one picture?

I want to take about 40 or 50 pictures and make it all saved andn put together as one picture.
Any app for an iphone or windows computer website/download?

Photoshop!

You want to layer a bunch of pictures together? You can do that with Photoshop if you have it but if you don't you can download the GIMP for free it will only take a little learning to use the programme

Do you mean like a panorama or a collage or a mosaic? Whatever you're trying to do, use Gimp. It's free but it takes a while to learn.

Hmm… You are wanting to do a collage for an iPhone (since you asked about an iPhone app). That screen is about 7.5 x 5 cm or 3"x2" big, yet you are wanting to squeeze 50 pictures into it.

Have you considered - even for a moment - just how incredibly tiny each photo would end up being?