While it's not really compression, resizing your pictures will save tons of space. I have a digital camera that I run in 12MP mode and it creates images that are approximately 4Megs in size. Because I am in Iraq with less than the best internet service available, emailing pictures of that size is just not gonna work. I perfer to use the Microsoft PowerToy
Image Reszier to resize my pictures quickly and easily. Once installed, it is integrated in the Windows shell so all you have to do is right-click on a picture (or pictures) and select resize image. A dialog is shown giving you the option to make the image small (640x480), medium 800x600, large (1024x768), or a custom size that you define. Image Resizer will create copies of the image in the size that you desire leaving your originals intact or you can choose to overwrite the originals thus saving space.
Just my two cents.
Derek