Unlocking the bootloader is not supposed to do that. It will wipe user data (/data partition) but I believe the internal storage ("virtual SD") should have been untouched. So you shouldn't blame yourself too much. And a nandroid would not have helped you as not only is that partition not backed up with a nandroid, but the default location for a nandroid is the internal SD, so it would have been lost, anyway.
That said, I try to backup any important personal data (even on partitions that are not supposed to be impacted) to my computer whenever doing something major like flashing a ROM or unlocking the bootloader. Only reason I've started doing that is a similar bug on the One X (EVITA) where actions that are not supposed to wipe the internal memory, occasionally did so (which is what I suspect happened to you).
I think your only hope is to use data recovery programs (Recova is a free one). But I've had mixed results doing so (and have seen similar reports here) when trying to recovery photos and other data that were "accidentally" deleted or recovered. Its certainly worth a try, and also keep in mind that you should do so ASAP as the more you use your phone, the higher the chance that those memory sectors where the photos were saved will be overwritten by other data.
Also, is there anything left on the internal memory at all when you browse with a file manager? Sometimes, corrupted data will be saved to a folder named LOST.DIR and there have times where folks have often found many of their photos simply moved there.
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Phone: AT&T HTC One (M8)
Tablet: Samsung Galaxy Tab Pro 8.4 (WiFi only)