They're the same command under the covers.
Imagescollide will check one image against another by writing the single image to a collision layer and checking.
CollideImage can write multiple images to the collision layer. Because you're testing the same images multiple times you don't get the benefit of Collideimage... I suspect.
If you need to do LOTS of collisions then search for Shifted Grid. I think there is a B3D (maybe a Bmax version) example on these forums.
Alternatively check the code archives for the customised 'shape' collisions (circle. rectangle/ elipse etc) as these will not be as accurate but quicker and, maybe, good enough. You could also try creating collision hotspots on your player and background so you can cut down the number of areas that need to be checked. Personally, I would the tilemap method if your current method doesn't give best results.
Imagescollide will check one image against another by writing the single image to a collision layer and checking.
CollideImage can write multiple images to the collision layer. Because you're testing the same images multiple times you don't get the benefit of Collideimage... I suspect.
If you need to do LOTS of collisions then search for Shifted Grid. I think there is a B3D (maybe a Bmax version) example on these forums.
Alternatively check the code archives for the customised 'shape' collisions (circle. rectangle/ elipse etc) as these will not be as accurate but quicker and, maybe, good enough. You could also try creating collision hotspots on your player and background so you can cut down the number of areas that need to be checked. Personally, I would the tilemap method if your current method doesn't give best results.