This is very simple.
Upwork's fees apply to everything.
If you work for one hour for a new client, then the fee Upwork collects is 20%.
If that client pays you a bonus, then the fee Upwork collects is 20%.
If you submit a receipt to a client for a photo license you purchsed to use on his website, then the client can use the "pay expenses" tool. Upwork will collect 20%.
If you don't want want Upwork to collect 20%, then you have alternatives:
a) Don't submit receipts. Don't get reimbursed. Simply charge more as hourly or fixed-price rates, so that your expenses are covered by your income.
b) Don't submit receipts. Don't purchase items. Ask the client to purchase the items directly. The client will log into the photo resource site and purchase the stock photo himself, and then he will send you the file.
Thanks. I would think that Upwork would have this topic as a support FAQ item. For most remote users, travel isn't a consideration at all but one opportunity I'm looking at would require a single upfront visit.