Xnview MP 0.75 has added "Join images" support accessible from Browser view
The "Join images" in XnView MP needs further support for:
1. Drag and Drop support on the main Join Images window from both MP browser and system explorer of Windows/Mac/Linux
2. Alpha transparency background option in the join images (PNG only)
3. Progress bar support for when joining larger images that take time
4. Saving and Loading of profiles/setting within the Join Images
5. Support for Effects such as the scattered mosaic Polaroid effect displayed in this previous post here- viewtopic.php?f=34&t=21594#p91023