You need to geo-reference your images to mosaic them. This could involve a lot of work as it is likely to require manual intervention. This can be done in qgis (Raster > Georeferencer) or by creating external reference files. See this question: How to batch-process georeferencing of rasters (prelude to animation)?

When you have geo-referenced your files, you can use gdal tools to create a mosaic http://www.gdal.org/gdaltindex.html or virtual raster http://www.gdal.org/gdalbuildvrt.html

These tools can be activated through the raster menu in qgis (Raster > Miscellaneous), but they run much faster from the command line.

You need to geo-reference your images to mosaic them. This could involve a lot of work as it is likely to require manual intervention. This can be done in qgis (Raster > Georeferencer) or by creating external reference files. See this question: How to batch-process georeferencing of rasters (prelude to animation)?

When you have geo-referenced your files, you can use gdal tools to create a mosaic http://www.gdal.org/gdaltindex.html or virtual raster http://www.gdal.org/gdalbuildvrt.html

These tools can be activated through the raster menu in qgis (Raster > Miscellaneous), but they run much faster from the command line.