These methods are 100%
lossless. Meaning NO loss in quality.
Step 1: Cut off any unneeded parts of the image. If the picture is of a couple hugging, remove all the bullshit such as the guy making a funny face in the background. Then proceed to the further steps.
Step 2: If you're using Photoshop, make sure you save all images that will be used on the web by going to File > Save for Web and Devices... and select PNG-24 (no dithering).
Step 3: Here, we have a 1.2MB PNG image. It's a picture of Hitman. (Could be way off.) Anyway.
That's one big picture for the web. Let's reduce the size of the image. Go here:
Smush.it and upload the image.
Smushit was able to save 0.12% of that image. Reducing 1.34KB of its size. Not much, but hey every byte counts.
For pictures under or at 150KB, use:
PunyPNG and upload your picture. Smush it first though!