[HTC One S] touch of jobo:
You can't do a hash compare, as the dump from your device is typically bigger than the image from the RUU, so it won't match. If you know exactly from which RUU the images on the device come (and you haven't flashed any special/extra partitions, you could do a byte-for-byte or line-by-line compare.

I did it a bit more 'visually'. If you see roughly the same stuff in roughly the same place, it is (most probably) the same kind of image. For example, these are not identical, but similar enough to know it's the same kind of thing, just a different version:

rpm.img from a RUU:

00006d00 40 30 06 00 70 b5 a8 20 06 f0 ff fd 1d 4c 07 23 |@0..p.. .....L.#|
00006d10 21 68 1d a2 05 f0 40 ff 21 68 1b 25 ad 01 49 19 |!h....@.!h.%..I.|
00006d20 c8 61 a8 20 06 f0 f1 fd 61 68 01 23 1a a2 05 f0 |.a. ....ah.#....|
00006d30 33 ff 61 68 49 19 c8 61 a8 20 06 f0 e6 fd a1 68 |3.ahI..a. .....h|
00006d40 09 23 19 a2 05 f0 28 ff a1 68 49 19 c8 61 a8 20 |.#....(..hI..a. |
00006d50 06 f0 db fd e1 68 03 23 17 a2 05 f0 1d ff e1 68 |.....h.#.......h|
00006d60 49 19 c8 61 a8 20 06 f0 d0 fd 21 69 05 23 16 a2 |I..a. ....!i.#..|
00006d70 05 f0 12 ff 21 69 49 19 c8 61 70 bc 08 bc 00 20 |....!iI..ap.... |
00006d80 18 47 00 00 24 a3 03 00 61 70 70 73 20 68 61 6e |.G..$...apps han|
00006d90 64 6c 65 72 00 00 00 00 6d 6f 64 65 6d 20 68 61 |dler....modem ha|
00006da0 6e 64 6c 65 72 00 00 00 6c 70 61 73 73 20 68 61 |ndler...lpass ha|
00006db0 6e 64 6c 65 72 00 00 00 72 69 76 61 20 68 61 6e |ndler...riva han|
00006dc0 64 6c 65 72 00 00 00 00 64 73 70 73 20 68 61 6e |dler....dsps han|
00006dd0 64 6c 65 72 00 00 00 00 70 b5 80 20 06 f0 95 fd |dler....p.. ....|
00006de0 1d 4c 08 23 21 68 1d a2 05 f0 f6 fb 21 68 1b 25 |.L.#!h......!h.%|
00006df0 ad 01 49 19 08 62 80 20 06 f0 87 fd 61 68 02 23 |..I..b. ....ah.#|
00006e00 1a a2 05 f0 e9 fb 61 68 49 19 08 62 80 20 06 f0 |......ahI..b. ..|
00006e10 7c fd a1 68 0a 23 19 a2 05 f0 de fb a1 68 49 19 ||..h.#.......hI.|
00006e20 08 62 80 20 06 f0 71 fd e1 68 04 23 17 a2 05 f0 |.b. ..q..h.#....|
00006e30 d3 fb e1 68 49 19 08 62 80 20 06 f0 66 fd 21 69 |...hI..b. ..f.!i|
00006e40 06 23 16 a2 05 f0 c8 fb 21 69 49 19 08 62 70 bc |.#......!iI..bp.|
00006e50 08 bc 00 20 18 47 00 00 24 a3 03 00 61 70 70 73 |... .G..$...apps|
00006e60 20 63 68 61 6e 67 65 72 00 00 00 00 6d 6f 64 65 | changer....mode|
00006e70 6d 20 63 68 61 6e 67 65 72 00 00 00 6c 70 61 73 |m changer...lpas|
00006e80 73 20 63 68 61 6e 67 65 72 00 00 00 72 69 76 61 |s changer...riva|
00006e90 20 63 68 61 6e 67 65 72 00 00 00 00 64 73 70 73 | changer....dsps|
00006ea0 20 63 68 61 6e 67 65 72 00 00 00 00 06 28 12 d2 | changer.....(..|
00006eb0 78 44 00 79 00 18 87 44 02 04 06 08 0a 0c 07 a0 |xD.y...D........|
00006ec0 70 47 08 a0 70 47 09 a0 70 47 0a a0 70 47 0b a0 |pG..pG..pG..pG..|
00006ed0 70 47 0c a0 70 47 0d a0 70 47 00 00 41 50 53 53 |pG..pG..pG..APSS|
00006ee0 00 00 00 00 4d 50 53 53 5f 53 57 00 4c 50 41 53 |....MPSS_SW.LPAS|
00006ef0 53 00 00 00 52 49 56 41 00 00 00 00 44 53 50 53 |S...RIVA....DSPS|
00006f00 00 00 00 00 4d 50 53 53 5f 46 57 00 3c 75 6e 73 |....MPSS_FW.<uns|

mmcblk0p10 from my device:

00006d00 bc 08 bc 00 20 c0 43 18 47 a9 00 08 18 04 62 70 |.... .C.G.....bp|
00006d10 bc 08 bc 00 20 18 47 a4 a3 03 00 40 30 06 00 70 |.... .G....@0..p|
00006d20 b5 a0 20 06 f0 d3 fd 1d 4c 07 23 21 68 1d a2 05 |.. .....L.#!h...|
00006d30 f0 14 ff 21 68 1b 25 ad 01 49 19 c8 61 a0 20 06 |...!h.%..I..a. .|
00006d40 f0 c5 fd 61 68 01 23 1a a2 05 f0 07 ff 61 68 49 |...ah.#......ahI|
00006d50 19 c8 61 a0 20 06 f0 ba fd a1 68 09 23 19 a2 05 |..a. .....h.#...|
00006d60 f0 fc fe a1 68 49 19 c8 61 a0 20 06 f0 af fd e1 |....hI..a. .....|
00006d70 68 03 23 17 a2 05 f0 f1 fe e1 68 49 19 c8 61 a0 |h.#.......hI..a.|
00006d80 20 06 f0 a4 fd 21 69 05 23 16 a2 05 f0 e6 fe 21 | ....!i.#......!|
00006d90 69 49 19 c8 61 70 bc 08 bc 00 20 18 47 00 00 70 |iI..ap.... .G..p|
00006da0 94 03 00 61 70 70 73 20 68 61 6e 64 6c 65 72 00 |...apps handler.|
00006db0 00 00 00 6d 6f 64 65 6d 20 68 61 6e 64 6c 65 72 |...modem handler|
00006dc0 00 00 00 6c 70 61 73 73 20 68 61 6e 64 6c 65 72 |...lpass handler|
00006dd0 00 00 00 72 69 76 61 20 68 61 6e 64 6c 65 72 00 |...riva handler.|
00006de0 00 00 00 64 73 70 73 20 68 61 6e 64 6c 65 72 00 |...dsps handler.|
00006df0 00 00 00 70 b5 80 20 06 f0 69 fd 1d 4c 08 23 21 |...p.. ..i..L.#!|
00006e00 68 1d a2 05 f0 f4 fb 21 68 1b 25 ad 01 49 19 08 |h......!h.%..I..|
00006e10 62 80 20 06 f0 5b fd 61 68 02 23 1a a2 05 f0 e7 |b. ..[.ah.#.....|
00006e20 fb 61 68 49 19 08 62 80 20 06 f0 50 fd a1 68 0d |.ahI..b. ..P..h.|
00006e30 0a 23 19 a2 05 f0 dc fb a1 68 49 19 08 62 80 20 |.#.......hI..b. |
00006e40 06 f0 45 fd e1 68 04 23 17 a2 05 f0 d1 fb e1 68 |..E..h.#.......h|
00006e50 49 19 08 62 80 20 06 f0 3a fd 21 69 06 23 16 a2 |I..b. ..:.!i.#..|
00006e60 05 f0 c6 fb 21 69 49 19 08 62 70 bc 08 bc 00 20 |....!iI..bp.... |
00006e70 18 47 00 00 70 94 03 00 61 70 70 73 20 63 68 61 |.G..p...apps cha|
00006e80 6e 67 65 72 00 00 00 00 6d 6f 64 65 6d 20 63 68 |nger....modem ch|
00006e90 61 6e 67 65 72 00 00 00 6c 70 61 73 73 20 63 68 |anger...lpass ch|
00006ea0 61 6e 67 65 72 00 00 00 72 69 76 61 20 63 68 61 |anger...riva cha|
00006eb0 6e 67 65 72 00 00 00 00 64 73 70 73 20 63 68 61 |nger....dsps cha|
00006ec0 6e 67 65 72 00 00 00 00 06 28 12 d2 78 44 00 79 |nger.....(..xD.y|
00006ed0 00 18 87 44 02 04 06 08 0d 0a 0c 07 a0 70 47 08 |...D.........pG.|
00006ee0 a0 70 47 09 a0 70 47 0d 0a a0 70 47 0b a0 70 47 |.pG..pG...pG..pG|
00006ef0 0c a0 70 47 0d a0 70 47 00 00 41 50 53 53 00 00 |..pG..pG..APSS..|
00006f00 00 00 4d 50 53 53 5f 53 57 00 4c 50 41 53 53 00 |..MPSS_SW.LPASS.|