Is it possible to do supervised image classification in QGIS? I require it for the estimation of cover management factor (C factor) in USLE
You can do supervised classification using the Semi-Automatic Classification Plugin. The plugin allows for the supervised classification of remote sensing images, providing tools for the download, preprocessing and postprocessing of images. You can download the plugin from the plugin manager.
It is also possible to conduct a supervised classification with a vary of algorithms (e.g. SVM, Random Forest etc.) from the Orfeo Toolbox (OTB) and SAGA. These algorithms are integrated in the Processing toolbox of QGIS. If you want to make a quick land cover or land use analysis the Semi-Automatic Classification Plugin is the first choice. But when you're looking for a comparative approach you should use OTB and SAGA because you can compare the results of processing based on different algorithms. And by the way you can configure a batch process within the Processing toolbox in case want to classify more than one image.