e-hentai's H@H has at least two different direct image url formats:

https:\/\/[\w.]+\.hath\.network(?::\d+)?\/h\/(?<image_hash>\w+)-.+;xres=(?<sample_size>\d+|org)\/(?<file_name>.+)
(simply https://{...}.hath.network/h/{image_hash}-{...};xres={sample_size}/{file_name})
If sample_size is not org, the image is resampled

https:\/\/[\w.]+\.hath\.network(?::\d+)?\/om\/\d+\/(?<image_hash>\w+)-.+\/(?<sample_size>\d+)\/\w+\/(?<file_name>.+)
(simply https://{...}.hath.network/om/{...}/{image_hash}-{...}/{sample_size}/{...}/{filename})
If sample_size is not 0, the image is resampled

On a side note: original gallery (but not exact page) url can be found by image hash using https://exhentai.org/?f_shash=.