Bridgit Field supports JPG and PNG images. Any other file formats within an album will be filtered out by the Bridgit Field app when clicking Choose From Library.
Live Photos - iOS Users
Live Photos is the default option when taking photos with an iOS device. These photos will use the file format HEIC and won't be available on the Bridgit Field app.
One workaround to covert these photos to JPG is emailing them to yourself. For more info on Live Photos: https://support.apple.com/en-ca/HT207310