While browsing, you can take a full-screen screenshot or use a built-in cropping tool to focus on a smaller area. If you wish to simply save an image displayed on a Website--without using the cropping tool--you can tap and hold the image to capture it, just like in Safari. Once you've captured a screenshot, you can add metadata such as a name, rating, notes, and tags.
Superstash's image library also lets you view and arrange your captured images. You can create folders to organize your images, as well as move, copy, and share multiple images at once, using the app's multiple selection tool. The app also includes some basic image-editing functions, like a pen and eraser tool, type tool, color picker, and clear tool.
Superstash costs $4 and runs on iOS 4.2 or later.