Image tips – including alt text
Ensure any images you use are copyright compliant. The Copyright and Creative Commons chapter of this book explains more about using Copyright and Creative Commons licenced material in your work.
Adding media guide from Pressbooks.
- Use high quality, large images whenever possible.
- Max size for a file upload into Media is 10 MB. Most images can be much smaller than that (250 KB to under 1MB) and still look good.
- For both a web and print book width 500px by height 600px is recommended.
- Centre images.
- Add a caption. Images without captions will not render properly in all e-readers.
- Set images to Full size in Pressbooks, otherwise a smaller or compressed version of the image will be exported.
- If you choose the Thumbnail option it will be 150 x 150px in the print version, which may be too small.
If the image view size is too small it can be hard to see details.
- Enable Lightbox under Appearance -> Web Options to allow images to show a larger view when clicked
- In your chapter, click to edit the image
- At Link To, under Display Settings, select Media File
- The URL of your image will be shown.
- Click Update to save the changes.
You will need to do this for any images you want to Lightbox.
Accessibility for images
Add Alt text to all images, unless they are purely decorative. W3.org explains alt text for different types of images.
Graphs, charts or diagrams will need to be explained in text. You can:
- Have the same information conveyed in the image in the surrounding text.
- Use Alt text if it is not too long.
- Use a long description. You can do this either in the text below the image or put it at the end of the chapter and use an anchor link. Anchor links for long descriptions instructions.
- Ensure you have a good contrast between the background colour and your font colour in charts, graphs etc. Black font against a white background provides the best contrast.
- Bold the font and increase the font size to increase the visibility in images.
- Don’t add tables as images (if you absolutely have to you need to fully explain it in the alt text or text description).
Our Open educational resources (OER) guide lists sources of images and explains how to attribute any Creative Commons images you use in your book.