What is a good, free way to scale a large batch of images down? They are of different sizes with the same aspect ratio. The target size is all going to be the same dimensions.
There are many programs that can accomplish the task of rescaling a large batch of images. Finding a good one for you depends on the details of your environment. Let's start with getting a little more information. What kind of device are you using? For instance, are you using a Windows PC, an iPhone, a Linux server, or something else?
PC
Since you are using a PC, I assume you are running either Windows or Linux. I will provide solutions for both operating systems.

### For Windows:

IrfanView is a lightweight, free image viewer and editor that supports batch processing. Here's how you can use it to batch-resize your images:

1. Download and install IrfanView from the official website: https://www.irfanview.com/
2. Open IrfanView and go to File > Batch Conversion/Rename.
3. In the Batch Conversion window, set the Directory field to the folder containing your images.
4. Choose a destination folder for the resized images in the Output directory for result files field.
5. Select Batch conversion and choose the desired output format (e.g., JPEG) from the Output format dropdown menu.
6. Check the Use advanced options box and click the Advanced button.
7. In the Advanced options window, check RESIZE and choose Set new size or Set new size as a percentage of original.
8. Enter your desired dimensions or percentage and make sure the Preserve aspect ratio is checked to maintain the aspect ratio of your images.
9. Click OK to close the Advanced options window.
10. Back in the Batch Conversion window, click the Start button to resize your images.

### For Linux:

You can use ImageMagick, a powerful command-line-based image processing tool. To install and use ImageMagick for batch resizing, follow these steps:

1. Install ImageMagick from your package manager. For example, on Ubuntu-based systems, you can run:

```
sudo apt-get update
sudo apt-get install imagemagick
```

2. Open the terminal and navigate to the folder containing your images using the cd command.
3. Run the following command to resize all images in the current directory to the desired dimensions (e.g., 800x600 pixels) while maintaining the aspect ratio:

```
mogrify -resize 800x600 *.jpg
```

Replace 800x600 with your desired dimensions and *.jpg with the appropriate image file extension.

These tools should help you resize your large batch of images quickly and efficiently.