Well, if you want to avoid the problem with the photography, you could sew on round beads instead. They should refract the light enough that you won't get black spots.
Of course, with any kind of sparkle or crystal on the veil, you could cause problems with the photography. Using round beads, they could catch the light of the flash and cause a flare in the picture if the angle is right.
Of course, the flat rhinestones, sequins, or crystals could do this too.
I do a lot of crafts, so the crafting part is trivial to me. Adding in thinking about the photography part leads me to this solution, if I were doing it -
I would probably use Swarovski round crystal beads. I'd use those because when you sew them, the thread goes all the way through so you anchor the bead in place a little better than if it only had one hole in the top or something. Much better to make sure you can hold the Mickey pattern with the beads.
Get two sizes - the smallest they make, and the next size up. Use two of the smallest for the ears, and one of the next larger for the head. And get clear beading thread for sewing them on - make sure it is NOT the stretchy kind.
I would put them somewhat sparsely around the veil. Less is more. Put enough so they will be noticed, but not so many that they are overwhelming, or that you get a flash of brilliance everytime the light hits the veil. That would be VERY bad at picture-taking time. I'd say put each Mickey-head no closer than 6 inches to the next nearest Mickey head.
Don't put them in rows or it will look like you have lines going around your head. They can't be just completely random either, or it will have a jarring effect. So, somewhere in-between. I haven't played with it, so I really don't know what the pattern of where the mickeys should go should look like. Maybe someone else would have a better idea on that.
When you sew each bead on, make sure that you stitch the thread back down through at the same place where you brought it up before going through the bead. If you do this, the thread should mould closely around the bead, and should be basically invisible. If you stitch down in a different location after going through the bead than you went through on the veil coming up before you went through the bead, the thread, even if it is clear (invisible) thread, may show some.
Finally, although you want to pull your stitches as tight as you can, you have to be careful not to pull them too tight. If you do, you will pucker the veil material, and ruin the effect. Also, since the beads have to be very close together for each Mickey head, you may be able to sew all three beads for a single head on before tying off a piece of thread. But never try tying off multiple heads on the same piece of thread. I know it will be a lot more time consuming to do it that way, but it's worth it in the end. If you connect multiple heads with the same thread, you run the risk of puckering the veil, even after the fact. All it takes is one good accidental yank on one of those connecting threads, and your veil will get all puckered up, and there may be no fixing it without taking out all the Mickey heads involved in the line of heads that got puckered up.
Also, when they are connected like that, you run a much bigger risk of losing beads. It's easier to break the connecting threads, and if you break one thread, you may lose several heads (however many are all sewn on the same strand).
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I know with all of that, gluing sound like a whole lot less trouble. And it is. But if you're gluing, just remember that the backside won't look nice. Depending on what material you are using for your veil, that may or may not matter. Most people use a tulle or another very sheer materiel, where you can see through the veil. If so, sewing is a much better option. If the materiel is a bit more opaque, where you can't really see the back of the crystal being applied anyway, then gluing should work just fine.
Just a word of caution.
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