I created a plugin for this feature, see http://www.highcharts.com/plugin-registry/single/5/Rounded-Corners
Edit 2014-05-07: Co-worker Stephane also has a nice drop-in code snippet for creating custom shapes: http://jsfiddle.net/highcharts/My9Qp/
The key is setting useHTML to true: http://jsfiddle.net/highcharts/8FSp6/.
Here’s another approach, allowing true SVG images: http://jsfiddle.net/gh/get/jquery/1.7.2/highslide-software/highcharts.com/tree/master/samples/highcharts/studies/axis-label-images/. The advantage of using SVG is that these images willl be visible in the exported chart as well.
An error occurred while saving the comment
An error occurred while saving the commentLevi Page commented
This is one of the things really lacking from HighCharts vs. AmCharts. Support for an additional Y-Axis Tooltip as well as a guide line between the chart tooltip and y-axis tooltip would be awesome.