I had always used Geogebra for this in the past, but now I’ve found this site, I don’t think I’ll bother with that any more. This has all the settings and options you need. You could get students up to the board to draw on where they think the enlargement will be prior to revealing it. Or show the enlargement but not the ray lines and they have to work out where the centre of enlargement is. There are also lots of nice examples to do on worksheets on the site. (click the home button)
One of the many good resources on the NGfL Cymru site. Shame they don’t exist as an organisation any more but luckily their resources live on!