Short of combining/moving them either in the phone with an app like ES File Explorer, or doing it through Windows Explorer or some other file management system, there isn't a native way to do that I'm aware of. Different apps are coded to store images in different places by default. You can combine images into one folder, but any new images will continue to be downloaded to whatever default folder their app determines. I haven't yet seen an app in the Play Store that will display all the images in one folder, although it's certainly a useful idea.
One other option, and I'm sure there are others, that you have is to use something like Picasa Web albums to store all your images in, and then access that service from your phone.