I was uploading images on this site on a blog post and I got annoyed when my site complained that the images size was more than 2 MB, yes that was the limit I had set. Uploading too big files on a blog post is not a good idea so I thought ok I will resize the images in GIMP but there were 7-8 files. A quick search online and I found this utility and I thought of sharing it with you.
Copy your images to a folder and run this command from within that folder.
sips -Z 1024 *.jpg
I think it will limit the largest side of the image to 1024px maintain the aspect ratio but you can also specify the height or width as well. Just make sure you work on copies of your images as this will modify the images.
Have fun.