If you are scanning photographs to show, then set the dimensions of the image scanned to a smaller size than what it is currently set to.

If you are taking photographs with a digital camera and moving them to a computer for posting, then open each one in a photo editing program (Photoshop, or what Bob H. suggests using) and change the image size to something less than what it is currently set for. (Experiment, this is why you see people posting a message that sez: test.

If you are using a cellphone camera, the iPhone is simple, because when you send it to your computer (email) you can select image size, use a smaller size option. Experiment. Android devices should have the same capability, but not certain how to do it.

These suggestions are just that, suggestions. Start experimenting! Just like in your youth.