"difficult to recognise" is correct and usable in written English.
You could use it in a sentence to describe something that is hard to identify or understand. For example, "The handwriting was difficult to recognise."
"It was difficult to recognise the team.
Often, it's most difficult to recognise what's happening on our own doorstep.
Why is it so difficult to recognise that the translator is as important as the two authors?
You have no idea how much that pleases me, especially when their reasons for responding to it are difficult to recognise.
The other gangsters (even the psychotic "Baby Face" Nelson) remain rather vague figures, difficult to recognise when seen briefly and usually in the shadows.
While Turkey's recent demonstrations were promptly explained away in terms of the "two Turkeys" interpretation, it has proved more difficult to recognise the coexistence of "two Brazils".
When we're taught to think of foreign sounds as English ones it becomes difficult to recognise the subtle nuances between them.
"The difficulty is that many ex-Séléka have taken off their fatigues and dressed as civilians … it's difficult to recognise these individuals," he said.
All pilots are trained to deal with such events, but one contributor to an aviation forum said the effects of such an incident "make it incredibly difficult to recognise and reach out for the oxygen mask and autopilot controls".
From the lowly minions to the towering bosses, every creature you killed was honed to perfection, its patterns difficult to recognise, its weaknesses veiled until the precise moment you needed to strike.
Singles become difficult to recognise, so meticulously reworked are they into new sounds that come jam-packed with instrumentals, riffs and electrifying guitar solos from Jetlag Johnson – extended versions that a standard studio album doesn't necessarily have room for.
