Compressing pictures

Picture editors usually aim for high quality rather than small size. In a web context, smaller file size is more desirable as long as the quality is still perceived as good by the human eye. 

There are many good compressors available, some as a desktop version, some as plugins for picture editors, and others online. compressor.io and tinypng.com are only two examples of popular online services. Typically, you have to upload your picture, and you can then download a compressed version of it shortly afterwards. This works well for JPEG and PNG, but with SVG the results can be mixed. Most online services are free for occasional usage.