One reason your images are so large is you are not cropping them -- you want to include only the currency, not the large "white" space of the entire platen. Regardless of where you post your images, you need to crop them properly. In most programs, the crop tool looks like a rectangle with a diagonal line through it. If you don't know, check the help in your imaging software.
Most modern scanners are capable of very high resolution, such as 600 or 1200 dpi (expensive scanners go even higher). These resolutions are designed for printing and are much too high for sharing on the web. For web images, the standard is 72 dpi.
It takes a little practice, but all of us here at SCF have managed to learn, so I'm sure you'll get the hang of it soon. Don't get discouraged.
In the meantime, if you want to continue to use 'off-site' hosting for your pics, this thread will give you a few tips...
https://goscf.com/t/11977KirkS