What you want to do exactly.
You've image and then you've write it in pdf file right.
you can write any thing in pdf files in asp.net by using iTextSharp
If you don't've idea on iTextSharp checkout links for sample codes.
and there is a open source pdf library for asp.net
checkout those two links you can get clear idea on handling pdf files in asp.net
you can add text,image and charts to PDF file.
Here you are using some tempfolder for saving charts right its better to use session variable or application variable for storing charts
It can easy accessable and easily deletable.
try steps mentioned in above links you'll get good output.