I've just noticed that Images I've made in photoshop have been saving at a smaller dimension. For example, an image made at 6cmx3xm is saving as something nearlly half the size?! I've tried saving as a JPEG and a PNG but both are having the same issue.
The true size of an image is defined in pixels, not cm. If you look at the size in cm, you have to take the resolution into account and maybe you changed that. For example: an image that is 600 pixels wide, will be 6 cm wide if the resolution is set to 100 pixels / cm. The exact same image will only be 3 cm wide if the resolution is set to 200 pixels / cm.