Pikelhaube type helmets were vary popular in various armies in the late 19th century, including the US army.

Furthermore, some countries had more than one army. The 19th century USA, for example, had the militia systems in every state and territory, as well as both the United States Army and the United States Volunteers during wars.

Germany had about 30 different kingdoms, grand duchies, duchies, principalities, and city states during this era, and even after the formation of the German Empire in 1871 their militaries retained their separate uniforms.

Some countries had very similar uniforms for all their military units, while other countries had vastly different uniforms for various units.

So a better image of the photo and closeups of insignia would be very useful.

Visually it is extremely difficult to really get details that would make this 'easy' to identify. So lets try a crowd intelligence approach via a community wiki?

The following is a best effort to describe what is identifiable.

This is currently quite incomplete. There is a lot of guess work involved and the current results are a bit contradictory. But since OP says that the image in question is all we going to get, this seems to be the best approach?

Please help improve this post!

Please edit in any details you might discern from the limited info we get from the pictures:

General description

This looks a bit sloppy: the fit seems to be not ideal, the soldier too small for the uniform. The belt isn't straight, the buckle rotated 5 degrees to the left, and the bands crossing the breast not centred. The belt hides to one half behind a right button of the tunic but obscures the corresponding button on the left. The two visible collars are also disorderly out of line.

A certain feeling bout this suggests the person may have been a bit drunk at the time. Maybe it's an actor in a costume.

Helmet

The helmet shape does not look Prussian/German. Spiked helmets called Pickelhaube were introduced in in Prussia 1842/43 and were even steeper initially, but then with lots of changes over the years made ever flatter.

Other nations like Great Britain, Russia, USA, Chile, Sweden/Norway have also used them, however shortly in some cases. USA seems to have had them the briefest, Sweden, Chile, UK still use them in ceremonial roles.

Sweden 1845:

USA 1881: ,
earlier:

First Prussian version:
(— The Waffenrock 1842 - 1895)

Model 1842 Preußen Infantry Landwehr Pickelhaube

Evolution of helmet shape in Prussia:

(Kopfbedeckungen- die Pickelhaube)

Small and obscure Landwehr units having different versions/shapes are not excluded by this. (example for Bavarian Landwehr)

But overall the helmet shape looks like those used in Great Britain (similar to custodian helmet). This is reinforced by the spike itself: Prussianhelmets would have more massive one and the earlier versions would be mounted on a much more visible metal cross about the cranial center.

Helmet emblem

Despite the enormous variation of those: Unlike any Prussian emblem I've ever encountered. Those Prussian versions (as well as most others that are connected or even subserviant to the Prussian army, like Reuss, Oldenburg, show a big eagle with spread wings, Saxony a star pattern, Bavaria, Baden and Württemberg a much more complicated 'logo'.

Of all German states, the closest match would be a quite imperfect one from Hessia.

(Die Geschichte der Pickelhaube)

Older Hessian version:

On closer inspection it looks like a wreath with a non-symmetric triangular symbol in the center and either two other smybols on top or a single symbol with a visual fluke of darkness in the middle creating the illusion of separation.
If it is indeed just one single symbol on top, then it might be a crown.
If it is a crown of that size and visual dominance, and this almost triangular shape that may be a harp then the closest match seems to be: Royal Irish constabulary?

(src, 1922 version)

(src: Explainer: Who were the RIC?)

But the weaponry with bayonet seems quite out of place for such a unit? The belt and buckle as well as the rest of the uniform seem also out of place for that.

Belt

Seems to be of white colour.

Belt buckle

Rectangular box shaped. Sign looks like an 'R'. (Most German version would have a round emblem on them]

Shoulder boards

These kind of epaulettes are not that common in Prussian/German uniforms, and usually reseved for officers.

Alternatives?

Trousers

Footwear

Tunic

Double breasted button-front that opens to the left!

This seems like either unheard of for Prussian uniforms, but the image could have been flipped?

Cuffs

Looks like a variation of 'Brandenburg' three button cuff, but buttons are small and quite widely spaced and it's over all quite sparsely decorated.

Rifle

• Long bayonet
• Two bands
  • One close to the muzzle
  • One past the sight
• End cap
• Rivet, screw or stamp, right side, below the rear of the sight.
• Action is not visible. Possible bolt handle above trigger.
• No visible magazine.
• What appears to be a lange vizier rear sight.
• Sling attached at the trigger guard and at the 2nd band.

At first glance it resembles a bit the 'Dreyse needle' with Dillenbajonett M/62 (Seems to be at least a specialised bayonet (to me: ~'Russian type', not a 'convertable knife' like Hirschfänger, Seitengewehr etc)?

The bayonet could be right. It's definitely a spike. The curve and band match. As for a Dreyse, that was my first guess, but it would have to be a variant. There might be that cheek in the stock for the magazine, it's hard to tell. The front band is too far forward. The sling is attached too far forward. The rear sight appears incorrect.