When you press the Win+PrtScr keyboard shortcut, Windows 10 will automatically save a screenshot of your computer screen or desktop in the Pictures\Screenshots folder. These images will be named in a serial order as Screenshot(1), Screenshot(2), Screenshot(3), etc. This screenshot index value or number is stored in the Windows Registry
Now even when you delete some screenshots, Windows will continue to name them from the last number onward. Say you were to delete Screenshot(2) and Screenshot(2) and you were to then take a screenshot, it will get saved as Screenshot(4). This would be the case even if you were to delete all the screenshots.
Reset Screenshot counter
If you take out a lot of screenshots and delete a lot, then this could become inconvenient.
If you wish, you can reset the screenshot counter, and make it start numbering from 1.
To do this, Run regedit to open the Registry Editor and navigate to the following key:
In the right pane you will see ScreenshotIndex.
Double-slick on it to open its Value box and give it a value of 1 in the Value Data field.
In my image below, you will see that it has a value of 4. I will have to change it to 1.
Having done this, exit the Registry Editor.
This will reset the screenshot counter on your Windows 10/8 PC. Now when you save images, the number 1 or the smallest available number will be used to save the screenshot.
See this post if Windows 10 / 8 is not saving captured Screenshots in the Pictures folder.