@vjrao96,
Sorry, replacing axis labels with an image or drawing shapes in place of labels is not possible as of now. However you can use unicode characters which is supported along with text. Please take a look at this Gallery Page for an example on adding unicode in indexlabel, which also works fine with other elements like axis label, legend text, chart-title, etc. Please refer to this Wikipedia page for list of unicode characters.
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Manoj Mohan
Team CanvasJS