Usually cameras provide settings that will allow you to shoot photos of smaller resolution, so if I wouldn't want images of that resolution, I would first look to change the shooting settings.
However when I want to batch resize images in mac, here is some of my techniques:
With an Automator Workflow
I have created an automator workflow of the following 2 steps:
- Ask for Finder Items: with Allow Multiple Selection.
- Scale Images: where I specify the desired dimension.
Then I click to run it, it asks me for the Finder Items, I select the images I want to resize and voila.
Note that the above 2 automator steps are destructive, meaning that your images cannot be reverted back to their original size. It's generally recommended to add an extra step in your workflow to copy the files before resizing them.
Using Photos Export
Another option using Photos, is to use the export feature and create your desired export settings to rescale your images. Then you can import them back.
Finally there is another tool I use it when I want to optimize jpeg files for the web: It is the imageOptim. It won't resize the images, rather than it will try to compress them even more, in order to save in weight.