Bottom Line — “Don’t be that person who uploads a 10mb thumbnail image. Compress it!”
I recently stumbled upon TinyPNG that has the ability to compress your images really well. The compression is lossy, but for the majority of the images I’ve processed, I couldn’t tell the difference. It works by “selectively decreasing the number of colors in the image” and supports png transparency. It also supports jpeg files.
When I’m developing websites, I need to keep in mind that not all my viewers will have high speed internet. Making sure that images retain a small file size becomes important. Another reason for having a fast loading website is that search engines tend to rank websites based on page load speed.
After creating an image, I run it through this service to get a smaller image out, and then I use it on my sites.
Don’t run an image if it contains private information information on it. Perhaps I’m just paranoid, but I prefer to avoid sending that to another server.
What about Photoshop’s “save for web” feature?
Apparently this feature in Photoshop is now considered legacy. It is no longer supported and has not been updated in ages. Although that was my go-to tool, I’d rather use newer compression algorithms.