Trimming unused blocks from a versioned image backup of a source storage that is stored in a sparse storage. In one example embodiment, a method may include identifying a versioned image backup that is stored in a sparse storage. The sparse may store first and second versions of the versioned image backup representing states of the source storage at successive first and second points in time, respectively. The method may further include deleting the first version, identifying a first set of blocks that were allocated in the source storage at the second point in time, identifying a second set of blocks that are allocated in the sparse storage for the second version, determining a third set of blocks that are included in the second set of blocks but are not included in the first set of blocks, and trimming the third set of blocks from the second version.