How to process XML Node data in XSL?

HI, I am new to XSL. I am wondering if there is a way to put some functional call in XSL to process xml node data. For example, There is a customer signature string(converted by my own rule) in XMl and I want it to be displyed as a signature picture through XSL. thx

xml is like this

<Myxml>
<name>
smith
</name>
<Age>
30
</Age>
<Signature>
kfdsadfhiosafw3riw3234werwqreksdf345324523453245
</Signature>
</Myxml>

and I have XSl file to present it. When the user click xml file, I would like they say the signature in picture instead of text string. I just did more research, now I know you could use extensive functions like VBscript in XSL for HTML page. But I am still not clear if you can use a method call which could convert the signature string into a picture and post the picture into HTML page. Any idea?