For starters, do not concatenate strings to build a SQL command. It leaves you wide open to accidental or deliberate SQL Injection attack which can destroy your entire database. Use Parametrized queries instead. This also means you don't need to convert numeric values to strings, in order to get SQL to convert them right back again...
Secondly, your image won't store properly even if you did get that working:
Why do I get a "Parameter is not valid." exception when I read an image from my database?[
^] explains what you are doing wrong with the image, and how to fix it.
Sort out those two, and your problem will likely go away.