How to create a cyanotype image in Photoshop in no time at all
Convert your image to monochrome using Image>Adjustments>Desaturate.
Add a new layer and fill with a solid blue (4e8aef) by going to Edit>Fill and choosing Color.
Finally, change the blend mode of this new layer to Linear Dodge (Add). Lower the opacity of the layer to 40% to reduce the impact of the effect.