Alt text (or alternative text) is an alternative for those who can not see the picture due to disability, poor internet connections or email client settings.
The alt text should describe the image so that even those who cannot see the image, still know why the image is there.
The alt text should be short (no more than 100 characters including spaces) and should not be descriptive of the image itself, but instead the function of the image. For example, if the image is a right arrow linked to the next page then the alt text should be “next page”, not “arrow pointing right.”
If you are using images without any specific purpose (i.e. just for show) you should still include an alt text. We suggest you then use – (a hyphen).
An image without alt text causes trouble for those using screen readers to read your mailing – they will then hear the image URL instead of directions or functions (as used in the example above).