Image Renditions Is a facility available in SharePoint 2013 for having different sizes of the image for different content holders? Different renditions can be created like full size, thumb nail etc. Image rendition also helps to adjust the picture to which part to display. This facility will help to reduce the size of the image to be downloaded at the client and hence optimize the performance. Image rendition also helps to store the file in the reduced space in the content database since only one copy of the file is actually getting stored. We need to enable BLOB cache before you can use image renditions.
A Rendition ID can be used with the image url like this “?RenditionId=n” to assign different rendition.