iPhone created Photos are now saved as HEIC files by default, so you will have problems if you want to view or edit them on a PC, so you have to convert the image first into a different image format.
However, you can set the iPhone to convert the HEIC files automatically to JPG format when transferred to the PC:
> Settings > Photos > Transfer to Mac or PC
Select the “Automatic” item.
You can also set the iPhone to safe the created photos directly as JPG files.
> Settings > Camera > Formats
Switch the camera recording to “Maximum Compatibility”.