Click on a raster layer in the QGIS table of contents, and then run this script. The corners of the bounding box of the layer will be printed to the console in the project's projection system. This is useful for supplying these values to Leaflet when using `imageOverlay`, which requires the top left and bottom right coordinates.

obtain_corners.py

from osgeo import gdal, osr
# Click on your layer in the TOC
alayer = qgis.utils.iface.activeLayer()
bag = gdal.Open(alayer.source())
bag_gtrn = bag.GetGeoTransform()
bag_proj = bag.GetProjectionRef()
bag_srs = osr.SpatialReference(bag_proj)
geo_srs =bag_srs.CloneGeogCS()
transform = osr.CoordinateTransformation( bag_srs, geo_srs)

bag_bbox_cells = (
    (0., 0.),
    (0, bag.RasterYSize),
    (bag.RasterXSize, bag.RasterYSize),
    (bag.RasterXSize, 0),
  )

geo_pts = []
for x, y in bag_bbox_cells:
    x2 = bag_gtrn[0] + bag_gtrn[1] * x + bag_gtrn[2] * y
    y2 = bag_gtrn[3] + bag_gtrn[4] * x + bag_gtrn[5] * y
    geo_pt = transform.TransformPoint(x2, y2)[:2]
    geo_pts.append(geo_pt)
    print x, y, '->', x2, y2, '->', geo_pt