The Flickr exporter converts all images to JPEG before uploading even when [Resize photos before uploading] is unchecked. For every export the Digikam console reports 'resized and saved to a temp file'. This is a problem for Animated GIF which is uploaded as a static JPG. For JPG this is also not ideal because the exported file is no longer bitwise identical to the source file, the checksums and filesizes of the uploaded files will not match the source files.
When you download the latest AppImage-5.5.0 can you see, it's already implemented. The Option "Upload original image file" have we added. See Bug 374441. GDrive from Gilles: https://drive.google.com/drive/folders/0BzeiVr-byqt5Y0tIRWVWelRJenM Maik
Thanks, that new option is there and I just hadn't noticed it.