You need some functionality that reads the data from the file and passes it to the BLOB (not BLOG). Depending on what your GUI is, you may already have such a feature, or you may need some function for that. It also depends on the answer to the question where the file resides - is it on the database server or the local client? If it is on the server, you could do something like this:
A DB2 UDB still image extender