If you cropped the screenshot to the relevant part not full screen, you should be able to post 4 provided the total isn't greater than 1024MB, where some of your screenshots are close to that, hence 4 posts.
I generally use the .png format and normally drop the True Colour to 24bit which reduces the size, without losing any clarity. The attached screenshot is under 35KB, you could also use the .jpg format which is usually a smaller file size.