Is there an app to save all your pictures?

I have a 16GB iPhone but my camera roll is full and I can't take any more pictures until a delete them, I deleted some of them like a month ago but the camera roll is full again and I don't want to delete any other picture, how do I pass all my pictures to like an account or something else that saves my pictures but that lets me see them on my iPhone?

Use a USB cable to your phone & save them on your computer. If they are precious photos, you should be doing backups anyway in the event you get a problem with the phone & all photos are lost.

You don't need an "app".

Connect the phone to your computer via a USB cable, and copy and paste them from the phone to your computer.

If they are not stored on your iPhone (taking space) then the only way to see them on your iPhone screen is via the browser after you have moved them to Dropbox, Flickr, Photobucket or one of the other services (making them private to keep others from seeing them) You can have access to them in the iCloud also, but deleting from your camera gets trickier because of the sharing aspects of iCloud.
I regularly connect my iPhone to a USB cable and store my images in various places on my Windows desktop machine, removing them from the iPhone when I do so, using one of the 3 or 4 programs under Windows, including just Windows Explorer and file copy.
You "only" have 16GB. You are going to have do decide what you carry around with you and where you keep the rest.

Just open windows exporer and cut/paste the entire block of them to your computer.