If you have created custom images for Wipe transitions, you can share them with other users by uploading them to:
kde-files.org, in the category Kdenlive.
Wipe images are greyscale images in the pgm format and can be used to transition from one track to another. Once a Wipe image file is uploaded to kde-files.org, it can be automatically installed by all Kdenlive users from the "Settings > Install New Lumas..." menu entry.
Sample luma image: