Add a Simple Folder Web-Part to Your Page
This web-part results in another type of image gallery with slightly larger thumbnails and operability than the standard image gallery web-part. It's also less configurable from a look/feel standpoint than the standard (non simple folder) image gallery web-part. For example there is no option to resize aspects of the layout, to change colors or opacity, or to add paging to the thumbnails if there will be many, many images in the gallery.
The benefit of this feature is that it allows you to just point it at a folder containing images and it does the rest, creating thumbnails, web size images etc. So the idea is that you organize the photos into folders on your local machine then upload the whole parent folder using an ftp client like FileZilla or whatever you use. The folder(s) need to be uploaded to Data/Sites/[SiteID]/foldergalleries folder, but from there you can nest them any way you want.
There is a feature for uploading files but the ftp approach is the sweet spot.