When you open an image in Photoshop, one of the following errors occurs:
It's important that the extension you add to the filename is the appropriate one for the actual file type of the image. When you choose a format from the Format pop-up menu in the Save As dialog box, the appropriate extension is added automatically. If you entered the extension manually, you could have typed in an extension that doesn't match the file format of your file.
If you cannot remember the actual file type the file should be, see Determine the file type of a document.
View your images in Finder or Windows Explorer. Check to see of there are two extensions on your files. If your images have two extensions, such as:
Remove the last extension so the file is named:
Open the problematic image in a photo app such as Preview (on macOS) or Photos (on Windows). Now save the file again as a JPEG image from within such an app. Try opening the file again in Photoshop.