If you use a microsoft windows computer, then you could download the free and excellent photo editor called 'paint.net' ------ it is really called paint dot net.
And see if you can open your images with it. They have file extensions with .jpg, right?
You can then also use paint.net software to resize the image to approximately 1024 pixels (width) by 768 pixels (height), and then try to upload again ...... using this method
shown here.