Photos that span the full width of a hub are only 520 pixels wide. That is not a very big image, so an image with really small text, such as yours, is not going to be legible. To get an idea of what an image will look like on a hub you can shrink the image down to 520px and set the zoom to "actual pixels."
Not sure if you know it or not, but when you upload an image, Hubpages automatically creates several variants. They create a 260px wide image for half-width images, a 520px wide image for full-width images and a 1024px wide image for your slideshow view. Someone reading your hub can click on the 520px wide image and it brings up the 1024px wide slideshow image which is large enough to be legible. What you could do is just add a caption beneath that image saying "click for a larger image."