IMG is the most common file name for images that come out of cameras, used in many phones and DSLRs, including the Google Pixel lineup. Google is looking to differentiate files created by the Pixel line's excellent cameras, though. Starting with Google Camera version 7.5, currently only available for devices running the Android 11 beta, image file names will start with PXL instead of IMG.
The new naming convention will also make motion photos appear right alongside the rest of the images. You'll no longer see them called MVIMG, but instead, you'll see something like PXL_20200819_155830631.MP.jpg. Similar changes have been made to Night Sight creations and portraits, now called something like PXL_20200819_162459593.NIGHT.jpg or PXL_2020_0820_132953656.PORTRAIT-01.COVER.jpg. That should make it easier to spot different kinds of photos just by looking at the file name. The same change is also coming for videos, though, which might be annoying as there's no way to easily tell videos and photos apart any longer when you don't see the file type.
Since this also changes how images are sorted on external storages or in cloud services, you might have to resort to renaming your images if you want to have chronologically sorted photos from multiple phones or cameras. The name change might also affect automated upload routines that rely on naming schemes, so keep that in mind once Android 11 makes it to your Pixel.
As mentioned, version 7.5 is only available on Android 11 at the moment. Sideloading the APK to a phone running Android 10 or older won't work, but if you're on Android 11 already, you can grab the latest release from APK Mirror. It's thus likely that the change will only come in full effect for everyone using Pixel phones once the update to the new Android release is rolling out later this year.
- and Brady