When Ally flags issues with a standalone image file, here is what each error means and how to resolve it.
Image Can Induce Seizures The image contains flashing patterns or rapidly contrasting lights that can trigger seizures in people with photosensitive epilepsy. This is a serious and potentially life-threatening condition. Do not use this image. Find an alternative.
Image Contains Text Not in the Alternative Description The image contains text that is not reflected in its alt text description. Screen readers cannot read text embedded in an image, so any meaningful text must be captured in the description. If the image is acting as text (such as a banner graphic), replace it with actual text. If it is a screenshot that includes text, make sure the alt text is descriptive enough to convey what the screenshot shows. In some cases, Ally will flag this automatically even when it is not actually a problem, so use your judgment to assess whether the description adequately covers the content.
Image Has Contrast Issues The image contains text with low contrast against its background. Upload the image into Photoshop or a similar program to increase contrast. If you do not have image editing software, you can use PowerPoint. Upload the image onto a slide, go to the Picture Format tab, and adjust the contrast using the Corrections dropdown. Then right-click the image and save it as a picture to export the adjusted version. Keep in mind there is no guaranteed way to know if the adjustment satisfies Ally's threshold, so use your best judgment.