A commonly used pattern to skip a displayed number of pictures is pagination.
Pagination solves a few UX problems commonly associated with skipping content:
- A reference point is needed. (Where am I now?)
- How do I get where I need to go (Where do I go?)
- On Mobile/Table devices it's important to limit the use of the keyboard when using navigational features.
By using an input box you're re-introducing these problems and many more. Thus each pictures needs to display a number of which pictures it is.
How do they reset it so it starts at the beginning again? What if they enter invalid data?
but more importantly:
Do my users need to skip a specific number of pictures?
or does it not matter? Is a general "show next 10" enough?
Familiarity is also a big thing to keep in mind.
It show also be noted that users don't know terms like offset or image number but everyone understands the concept of pagination. (Next page, previous page, if I have 10 showing and click page 5, I'll skip the first 40)
The concrete answer to the question: "What is the Appropriate wording for the input box users use to navigate images" is: It depends on how you prefix your images.