Allow images only
The Allow images only option is only applicable for the File field. It allows users to upload only image files instead of any other file type.
When you select this option, you can specify the File size limit by selecting the minimum and maximum MB. This will prompt the user to upload an image of the specific dimension on the entry page.
Additional Resource: You can check out the Validations guide to learn more about the several types of validation that you can set up on a field.
If you want to make changes to any field’s properties, make sure you go through our Content Type Change Management guide to avoid data loss.