Identify helmets from LEGO Bionicle

Question

I found these LEGO Bionicle helmets when looking through a box in my attic. I want to identify the corresponding sets.

Answer 1

Top-left is part 50931 "Bionicle Head, Toa Hordika Vakama", which appears in two sets in dark red.

Next to its right is 53584 "LegoBionicle Mask Ignika (Vezon)". Judging from the colour, I'd say it's from set 8764-1.

Next is 52806 "Bionicle Head, Toa Hordika Matau" from set 8740-1.

Next, I cannot identify the green (lime green? bright green?) spiky one, but fellow user Sander de Dycker identified it as 57553pb01 "Bionicle Head, Barraki Ehlek with Marbled Lime Pattern", in transparent green, which appears in two sets.

Next is 52818 "Bionicle Head, Toa Hordika Onewa" from set 8739-1.

Next one is too dark in the photograph to tell apart any identifying details. But fellow user Matthew Jensen thinks it might be 50927 "Bionicle Head, Toa Hordika Whenua" from set 8738-1. It's difficult to be 100% sure without a better photograph, though.

Last one on the top row is 78180 "Bionicle Mask Jutlin with Black Top (Shapeshifted)" from set 8691-1.

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Bottom row. First is part 50931 "Bionicle Head, Toa Hordika Vakama" (same as top row) in dark green, from set 8940-1.

Second one is 64786 "Bionicle Mask Suletu - Flexible Rubber" from set 8731-1

Next is 45682 "Bionicle Mask Huna (Toa Metru)" which appears in 7 sets.

Next one is 46479 "Bionicle Mask Ruru (Toa Metru)" in dark blue, from set 8940-1.

For the next one, I wasn't able to find any masks/heads in orange with brown on top. Fellow user Sander de Dycker pointed out that it's dark red with orange in the face, instead: part 57531pb01 "Bionicle Mask Arthron with Orange Face" from set 8911-1.

Last one in the bottom row is 78570 "Bionicle Mask Radiak with Black Top" from set 8947-1.

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In general: Doing a reverse image search from a cropped portion of the photograph usually yields good results, but it's easier to do when the photograph is taken with a white background, good lighting to minimize shadows, and closer up (macro photography would help a lot). Unfortunately a carpet background doesn't help much, as happens with the black mask/head.

Otherwise, bricklink searches for "bionicle head" and "bionicle mask" with the advanced search option of filtering by colour do provide short lists of parts which are quick to look through. The downside is that one needs to know the exact lego colour of the part, which is not always an easy task (as happens with the bright green spiky one and the pearly orange one).