Our system runs initial checks on images as they are being uploaded and there may be times when you image will not upload to the media library. It could be the image size, the file format, etc.
But, if you have seen the error message "Error occurred during file upload" (seen below), it typically means that there is an issue being introduced with how the image file is being saved with certain tools.
The image file is not corrupt, per se, but it does not work in its current format/compression with our database guidelines.
To correct this error, you can open the image in any image editor. Re-save it in a different format. For example, if your current image is a jpg file, re-save it as a png. Then, try to upload into the media library again.
See these related help articles regarding supported images and file limitations.