public static int insert_value(string image_name, string image_path, string image_upload_time, string image_upload_date, string status)

It's declared as a method returning an integer value - but the compiler can see a path through the method where no value is returned, and no exception is thrown.
This would mean a problem at run time, so the compilation fails.
The normal reason for this to forget the "return x;" at the very end, or to miss out the value with a return statement completely; or to have intended the method to not return a value at all. In the later case change the definition to:

public static void insert_value(...

Have a good look at the code - it should be fairly obvious.

And please, try to follow C# naming conventions, which do not include underscores: the method should be called InsertValue, not insert_value