You need to indicate that your application can open image files. This is done in Info.plist:
<key>CFBundleDocumentTypes</key>
<array>
<dict>
<key>CFBundleTypeName</key>
<string>Images</string>
<key>LSHandlerRank</key>
<string>Alternate</string>
<key>LSItemContentTypes</key>
<array>
<string>public.image</string>
</array>
</dict>
</array>
"" . , , application:openURL:sourceApplication:annotation:. URL .