I have a lot of photos emailed to me and they are usually sent to me in a smaller file size than the original. I will first say it is faster to email your photos in a smaller file size but don’t delete or change the original file size. Generally, speaking a digital camera will save the original images in a large file 1000 KB or higher (example of the photo size in pixels: 30×40 at 72 dots per inch). This will fluctuate depending upon your cameras settings and size mega pixels; ALWAYS set your camera to max capabilities.
When you resize or resave an image it gets compressed and you will lose image quality. I recommend that you always save your original files in tiff and if not use jpeg/jpg but make sure you don’t resave the original jpg image file. If you resave a jpg you will compress the image every time you resave that same file, this will cause your photos to lose quality.
In the printing world and for your viewing pleasure, you need large files. Every image will be converted to 300dpi thus small compressed files will not work. The moral to the story is make sure you save the original file and make another image file if you are going to resize the image.