To demonstrate how to use the Clipper tool in QGIS 2.8.1 to clip out a section of a GeoTIFF image.
Add the georeferenced raster image. Go To Raster > Extraction > Clipper
In the Clipper dialog box, name the output file. For the demo, Extent Clipping mode is selected. Select the extent by dragging the cross cursor to form a square around the area that is to be clipped out. Once that is done, the extent coordinates will automatically appear in the dialog window. Click OK.
A Processing completed message box will appear. A new raster layer will appear on the Layers window.
Right Click on the new layer > Zoom to Layer. The layer will appear in view.
The new layer may not have copied the correct CRS from the layer it was clipped from. To adjust the CRS, Right Click on the new layer >Set Layer CRS
In the dialog box, select the corresponding CRS. For the demo, Minna/Nigeria West Belt is selected.
Zoom to layer and observe the layer is now displaying the appropriate coordinates.
Thank you for the audience.