In my opinion, this album category should be moderated by someone or several people, who have the power to edit, remove and group the pictures. Otherwise pictures will come in of plants with strange symptoms along with an unconvincing claim that nutrient deficiency x, y, or z caused the symptoms.
It is not easy to establish that a given set of symptoms are caused by a lack of a specific nutrient. Toxicities can cause symptoms. There could be multiple deficiencies. Plants can look sick sometimes for other reasons. (If you didn't know about deciduous trees losing their leaves in the fall, you might think they were suffering from some gastly, terminal deficiency---"My tree is dying! the leaves are all turning yellow and falling off!! I have fertilized it with a nitrogen ferterlizer, but the tree just keeps getting worse!! HELP!!!!)
In order to show a nutrient deficiency and be reasonably sure you really HAVE that deficiency, you should have all other nutrients but the deficient one in good supply. How do you know this? That is not easy to answer. Just through long-time experience, I guess. You also have to cure the deficiency with an addition of the deficient one and that one only. If you must use a two-nutrient salt to cure the deficiency, such as KNO3, you should be able to argue, for example, it must be the nitrate that is curing the deficiency because the deficiency looks nothing like K deficiency which is damage and holes in the older leaves, and, besides, my potassium test kit shows I have plenty of K in the water.
It also helps to be familiar with pictures of deficiency symptoms of crop plants that can be found on the web. At least for the macronutrients , deficiency symptoms of aquarium plants are similar. Iron and the micros might be another story, although I have seen boron deficiency in aquarium plants that resembles pictures and descriptions of B deficiency in crop plants.