Consider an image created by imaging software (such as Acronis True Image.) Can Avast successfully scan the files while they are in this form?
Should work if you mount the image. There needs to be a decoder for a .tib, just like any packed binary file.
Yes, avast have such capacity (unpacker).
It might try to scan it in its raw format, which could return some strange results (weird data strings from compression, etc. aside from it probably taking a long time because of their size. I exclude my drive image Folder, though I should probably further limit that to the *.v21 file types in that partition/folder, in case something else got in there.
I always do an avast, SAS and MBAM scan before creating a drive image to try to be a sure as reasonably possible that the data going into a v21 file is clean.