The checksum for the Nexus 7 Wi-Fi images are available below for the first generation Nexus 7.
Version: 4.1.2 (JZO54K)
MD5: d906b505ccae0d439839d3c5fafb137a
Version: 4.2.0 (JOP40C)
MD5: e681477b3babbafb6fc6891438a254e9
Version: 4.2.1 (JOP40D)
MD5: 27a9a10cfc75b100ba63afa35c08f3db
Version: 4.2.2 (JDQ39)
MD5: b869c77ba7e2929b3ca00804bf64b945
Version: 4.3.0 (JWR66V)
MD5: 77e304584c4f192761234a9e1eb2fbe3
Version: 4.3.0 (JWR66Y)
MD5: 30eb362b494211164d8a8a6756419e57
Version: 4.4.0 (KRT16O)
MD5: c9fc3764ab268962424b38e75b26d875
Version: 4.4.0 (KRT16S)
MD5: b8d77fa080e2d71f4366a23df6d3ecaf
Version: 4.4.2 (KOT49H)
MD5: 22ac4dcf402f30a3a891192dfdb714df
Version: 4.4.3 (KTU84L)
MD5: 544edcc5547ba622a8bf13c428e06508
Version: 4.4.4 (KTU84P)
MD5: 176a1561f322e86216b7edaaa4b2c6bf
Version: 5.0 (LRX21P)
MD5: e68948c23c918436680bd28fc6aaf983
Version: 5.0.2 (LRX22G)
MD5: bd50cf99c92704366c90be7a2ba6c7d9
Version: 5.1.0 (LMY47D)
MD5: f7deb9350354f7b3717fcfdeedc72521
Version: 5.1.1 (LMY47V)
MD5: 32624479e2f24d07fd04a2099a163604
If you require the images once more, they can be acquired from developers.google.com.