What is the meaning of "// Image base:" in an assembly manifest

I am trying to take a .NET C# DLL hash and want it to be same there has been no code change. When I decompile the DLL I see a "// Image base:" entry at the end which keeps changing. Example (The last line):

// Metadata version: v4.0.30319
 ----
// MVID: {7C2770DB-1594-438D-BAE5-98764C39CCCA}
.imagebase 0x00400000
.file alignment 0x00000200
.stackreserve 0x00100000
.subsystem 0x0003       // WINDOWS_CUI
.corflags 0x00000001    //  ILONLY
// Image base: 0x00600000

What does this // Image base mean and how can it be made a predictable value?