A JPEG image can be reduced in quality and, thus, in file size using ImageMagick in a way such as the following:
convert -quality 85% image.jpg image_small.jpg
How can the quality of an image be reduced such that the resulting image is below a certain file size (e.g. 3 MB)? A scenario in which this would be useful would be preparing a large number of images for upload to a site like Imgur.