God created man and Man created Gods is the adage. It is not strange that Gods descended at the end of every eon, yuga to restore dharma. Sri Rama and Sri Krishna are the avatara purushas who are deified and worshiped even today. Rama from Ayodhya and Krishna from Mathura, besides Devi Kamakhya in Assam, are examples. Since divinity is inherent in all jivas, anybody can rise to Godhood. It is common practice to pay obeisance, respect to parents, elders, guests as Gods! Many Gods are thus said to be born in Bharata.
Idol worship is common in Southern States of India/Bharata. Huge impressive temples with Gopuram (seven floor levels) are built by Kings and rich landlords, or even common pious people who collect donations and help build temples. Idols of Gods and Goddesses are carved and installed with sacred mantra of consecration in these temples. Consecration or pranapratishthapana is a common practice before istalling idols and worshiping them. This is just touching ones own hand on the chest as also on the chest of the idol and chant the sacred mantra, thereby, the prana /life-force (vibrating heart-beat) is reverberated and the idol is consecrated, as if, turning the idol into a living God!
Instead of worship of the idol, shalagrama worship is found in many northern and eastern parts of Bharata Khanda (Indian Sub-continent). Huge impressive Temples with seven storey Gopuram are constructed and beautiful idols of Radha and Krishna, Rama, Sita, Lakshmana Bharata, Shatrughna, and Hanuman, Lakshmi Devi, Sharada Devi, Annapurneshvari Devi, and many others are found through out the country. We have famous temples like Belur and Halebid, Somanathapura known for architectural excellence with carvings on pillars and the deity Chennakeshava. Tirumala Tirupati Venkateshwara, Thiruvananthapuram Ananthapadmanabha Swamy, Kanchi Kamakshi, Madurai Meenakshi, Badami Banashankari, etc. are important pilgrim centres. The temple towns like Somanatha, Dwarka, Mathura, Varanasi, Ayodhya, are only a few to mention. The list goes on, and on.
Entire India/Bharata Khanda is traversed by Gods and Goddesses and people have made their idols and worship them. We have the Sri Ram Temple in Chunchankatte (25 Km from Mysore) where He is said to have resided during exile!, There are Sculptors who get darshan and carve out idols from memory. Karnataka is said to be the laboratory, workshop, with specialists-sculptors. Jakkanachari has sculptured the idols of Vishnu in Belur and Halebid temples. Thus, we have knowledge and technology of temple construction on scientific and agama shastra rules and regulations. These are dated back to thousands of years and an example is that of a Vishnu temple at Halsi, near Belagavi constructed during the Kadamba dynasty with a stone inscription inside the temple. There is thus a long history of Temple architecture and their sculptors (who have presented us the Belur, Halebid, Airhole, Pattadakal, etc.).
What is 'Pranapratishtha'? whey, where and how is it done? These are questions that are to be answered by specialists who are well-versed in agama shastra, Veda and Upanishads. We have the Pancharatra agama shastra as the basis of all yantra, mantra, tantra and ways of propitiation of Gods. Some people practice worship of selected Gods and perform yajnya yaga, havan, homa, and other rituals to attain siddhi and use that power for welfare of common people. There are good, as well as, evil forces, for both welfare and destructive purposes! Society is full of good, as well as, wicked people, who exploit the innocent for their own material benefits. People in distress look for guidance and may fall in trap! Hence some one should guard them and help them.
Now, coming to temples, idol worship, and consecration of idols (Pranaprat08ishthapana), there are ancient scriptures that give detailed methods, vidhi, vidhana. However, it should be noted that, this is restricted to only a section of the people who worship idols. Not all are idol-worshipers. May be, it is the Dravidians of Southern India who practice this? There are thousand of temples with varieties of idols of many a different Gods and Goddesses all over the South, i.e, south of Rivers Narmada and Tapti.
The practice of worship of shalagrama (Basalt/Black Stones) stones found in the Gandaki River. We find some persons selling these stones at exorbitant prices in Star hotels, fooling mostly the innocent tourists! These shalagrama stones are having holes with imprints of molluscs, snails, and jelly-fish-like creatures. They call it by names like Narasimha shalagrama, Vishnu Shalagrama, etc. and worship them. it is also warned here that shalagrama puja has many restrictions. at least, a spoonful of clean water and a Tulsi / basal leaf should be offered daily with utmost sanctity. Also, it is said that not all shalagrama are benevolent; it is thus subject to conditions as advised by pundits.