I posted a slightly different query as my answer to a quiz question (SQLServer Quiz 2011).
This query is modified to query SSRS 2008 and to return the actual parameter values used for a specific report. Might be helpful, too.
I agree, the image data type is not the one someone would expect to find such valuable information. It's also strange that MS still uses the text/ntext data type in SSRS 2008 even though they advice against it in (almost?) every single offical documentation.