qtbase/src/gui/text/qtextformat.cpp contains the following Qt 5 to-do comment:

// ### Qt5 qreal replace with a QTextLength
/*!
    \fn qreal QTextImageFormat::width() const

    Returns the width of the rectangle occupied by the image.

    \sa height() setWidth()
*/

If this can be done without impacting source-compatibility, it should be done for Qt 5.0.0. If not, the comment should be either removed or changed to a Qt 6 to-do.