The alt image attribute is necessary as it tells Google what your image is about. Without this alt tag, Google would not know what your image was about and might take inference about the photo's subject from surrounding text. This tag is also useful for helping a vision impaired person to understand what's being shown in the image. For all it's good points, the image tag can be abused. You should never keyword spam in an image tag, but only use words that are necessary to describe the image. Share your point of view?