If you add an image to the document library and replace it with a new image, the image does not update. The reason is that image is added to the cache and does willingly update. For example: <img data-sp-originalimgsrc="/Shared%20Documents/replacedImage.png" alt="" src="blob:https://x.sharepoint.com/{guid}" class="CSS-100" width="1000px" height="250px"> keep showing the old image because the blob cache does not update.
How long it takes until the blob cache is updated?
The image should be updated as soon as it is edited in SharePoint. For example, you could add the modified date to the URL to force the cache to show a new image. Ie: blob:https://x.sharepoint.com/{guid} should be blob:https://x.sharepoint.com/{guid}?{lastupdatetimestamp}
