When we try to insert an image to Resolution field of a knowledge document, an error "File attachment 'xxx.bmp' has a prohibited file type. Please choose a different file." appears as shown in the following screenshot and it fails.
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Out-of-the-box, inserted images of knowledge documents are stored in "Quick Upload" folder under "Images" Repository. As a default, only *.gif, *.jpeg, and *.jpg files are permitted to store into the Repository.
In order to insert the *.bmp or another image file type, you need to add its extension to Prohibited File Types list of the Repository as per below.
<Please see attached file for image>
<Please see attached file for image>