Just for easy googling later. As of now here’s what the source code has:
/**
* Add an image inline with the text.
* Usage: Before image <img id="MyId"/>, after image.
*
* A width and height can be specified.
* By default the width and the height is the same size as the font height.
* Use "desired" to use the same size as the image brush.
* Usage: Before image <img id="MyId" height="40" width="desired"/>, after image.
*
* A stretch type can be specified. See EStretch.
* By default the stretch type is ScaleToFit.
* Usage: Before image <img id="MyId" stretch="ScaleToFitY"/>, after image.
*/
class FRichInlineImage : public FRichTextDecorator