Your custom input profile must somehow be assigned to and/or used with images that come from that scanner or camera. There are several possibilities that may be encountered when opening the image in Photoshop, depending on the particulars of your scanner/camera and its associated software. Each situation requires different treatment. There are basically four possible scenarios, shown here:
Does the image have an embedded profile?
1. Your Digital Camera or Scanner does not embed any profile into the image.
If the image has no embedded profile, then when you open it in Photoshop, you will see this dialog:
Use the pop-up menu to select the proper custom input profile. It is further recommended that you convert to the working space by using the checkbox as shown above.
If the software that controls your camera or scanner is able to embed your profile into each image, then by all means, do this. When you open the image in Photoshop, you will see this dialog:
In this case, we recommend that the embedded profile be used to convert the image into your working space, as shown by the selection made above.
Some capture software always embeds a generic or standard profile into each image, such as sRGB. If this profile just happens to be the same as the profile you have selected as your RGB working space in Photoshop's Color Settings dialog, then the image will open without any intervening warnings or dialogs. But the wrong profile is associated with your image and this must be remedied. Note that this would be a rather unlikely (but nevertheless possible) coincidence. In this case, the incorrect profile must be removed and replaced with the proper one, which involves a couple of steps.
After you have opened the image in Photoshop, you must assign the proper profile by selecting Image / Mode / Assign Profile… and then select the custom profile from the pop-up menu:
Then you should convert into your RGB working space by selecting Image / Mode / Convert to Profile…:
2c. Your Digital Camera or Scanner embeds a profile into the image, but not the right one.
If your capture software has embedded a generic or standard profile into the image (but not the same as your working space), this incorrect profile must be removed and replaced with the proper one, which involves steps similar to the previous situation above. When you open the image in Photoshop, you will get this dialog, which allows you to remove the unwanted embedded profile:
Now you must assign the proper profile by selecting Image / Mode / Assign Profile… and then select the custom profile from the pop-up menu:
Finally, you should convert into your RGB working space by selecting Image / Mode / Convert to Profile…: