A large part of my job is hiring, supervising, managing, etc. so I'll throw in my 2 cents. I don't think you should pass over reference to the digital imaging because it can look as though you didn't read the job description well enough, but neither should you address it on your resume or as a lack of skill. In your cover letter, mention it in a postive, "I'm really looking forward to learning this skill" kind of way. Along the lines of "I note that digital imaging will be part of my job, a branch of artwork that I find very exciting, and I look forward to adding this skill to add to the array of experienced artistic skills I would bring to this position." In your own words, of course. I haven't had my morning cuppa yet so not at my best.

Edited to add: Good luck with the application and really hope you get the job.