There are times that you may need to compress image files to reduce the time it takes for those images to load on your webpage. The fewer bytes the browser has to download, the faster the browser can display them to the screen. In a case of adding background animations to a page, the browser needs to be able to download the photos rapidly, optimizing the performance of your webpage. Here are a few helpful links that can help you compress your image files prior to uploading them to your webpage. 
Online versions:
1. Compress Now - A free online service that lets you upload images from your computer, choose a compression percentage and download the optimized image. It supports GIF, JPG and PNG formats. The service also allows the drag and drop of multiple images from you computer, with a max upload of 10 images and a max individual file size of 3MB.
2. Compress JPEG - Allows you to quickly compress JPEG, PNG and PDF files online. You can select up to 20 images to upload or simply drag and drop. Compress images separately or group them together in one ZIP file. 
3. Image Optimizer - Lets you resize, compress and optimize your images, and it's available as either a free online service, a free desktop application or as a paid upgrade to remove the promo text at the bottom of optimized images. It's simple to use and allows you to choose the resulting optimization quality, max width and max height. You can compress images in bulk and view the progress of the optimization.
4. Website Planet - Allows you to compress your image files (jpeg or png) while keeping the quality while decreasing the size. 
Downloadable versions for your desktop:
1. Shrink O'Matic - An Adobe AIR application to batch and resize images easily, handling JPGs, GIFs and PNGs. Drag and drop images into the app and they will be resized. You can customize the settings and choose the output sizes, rotation, name, location, format and watermark. It supports EXIF data so you won't lose any information once the images are processed.
2. RIOT(Radical Image Optimization Tool) is a free program to optimize images for the web efficiently. It includes an easy-to-use interface to compare the original with the optimized image in real time, so you can instantly see the resulting file size. The program is lightweight, fast and boasts powerful features for more advanced users. It supports various formats and features automatic optimization that selects the most suitable format and parameters.

3. PNGGauntlet - Lets you optimize PNG files and is available for Windows. It combines PNGOUT, OptiPNG and DeflOpt to create the smallest file sizes possible, with no reduction in image quality.The program converts JPG, GIF, TIFF and BMP files to PNG, and gives individual progress bars for each file, highlighting the file that is currently compressing, and a status bar to keep track of the total bytes saved.