punypng is a free tool that dramatically reduces page load times by reducing the file size of an image without any loss of quality. punypng uses several web optimization techniques to reduce the file sizes of your images. It first analyzes the content of your image and figures out the best image format to use.
Depending on the file, punypng will automatically convert your GIF into a PNG format and then further compress that. For JPEGs, sometimes it’s better to make it a PNG, and other times it’s better to keep it as JPEG and use jpeg-tran to optimize it. punypng makes all those decisions for you and ensures the best possible results.

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Lazy loader is a jQuery plugin written in JavaScript. It delays loading of images in (long) web pages. Images outside of viewport (visible part of web page) wont be loaded before user scrolls to them. This is opposite of image preloading.
Using Lazy loader on long web pages containing many large images makes the page load faster. Browser will be in ready state after loading visible images. In some cases it can also help to reduce server load.
There are options for control maniacs who need to fine-tune. You can set threshold on how close to the edge image should come before it is loaded. You can also set placeholder image and custom event to trigger loading. You can check out the demo with FadeIn Effect enabled.