One way is compressing the image, which reduces file size without having to resize it. Image quality will suffer as you increase compression and start losing more data.
Another method is to resize your photo, decreasing the pixels it takes to store the image. Reducing image size doesn’t reduce image quality, although it may lose small details.
Photos from modern cellphones and cameras usually have over 6 million pixels, while most cellphones, tablets, notebook or TV screens have only about 1.5 million pixels, which means you end up seeing a resized version of the image (you only use the full image if you print it). So if you resize your image, decreasing its width and height to a half, your image would have about the same number of pixels as the screens that will display it, and you wouldn’t be losing any quality or detail, even looking at your image in full screen mode.
If you have a huge photo, we recommend resizing it to about 1900 by 1100 pixels, with JPG format and 90% quality. You will get a versatile image with great quality, that you can send to anyone without taking too much time.