Hi Emily,
I'm sorry to hear about your situation! I think a vacuum cleaner would be a good solution, but I agree that a standard vacuum may have too strong of a pull. If you do have access to a vacuum with a hose, you might be able to dampen the suction enough by covering the end of the hose with a piece or two of fine mesh (like a nylon stocking) secured tightly with a rubber band. If you try this make sure you fully open any bleeder valves that the vacuum may have, and test the suction on a scrap of paper (or similar) to see what kind of pull you're getting. I feel like a vacuum may be the best option if you have fine particles, since the suction should lift them straight off of the surface.
How large is this photograph? If the print is small enough to be handled easily, you might be able to flip it over and let the particles fall onto the ground, and then use a very soft brush along with gravity to knock them off of the surface. This would not be suitable for a larger item, and I would recommend this strategy as a two-person job to ensure careful handling.
If neither of these options would work for you, I think brushing the particles off of the surface using a very soft bristle brush will be your best option making sure that you are using the lightest amount of pressure to lightly pick up and sweep the glass away. You could sweep up the glass in small batches onto a sheet of paper to minimize moving the glass particles across the full surface of the photograph. This could be helpful if the print is larger.
I hope this helps!
Best,
Jen
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Jen Hunt
C2CC Forum Monitor
Special Collections Conservator
Hesburgh Libraries, University of Notre Dame
jhuntjoh@nd.edu------------------------------