As with many others I too am fed up with istock and their changes in pricing/credits.
Yet again they have devalued my investment and I can't see how it can be legal.
Example, invest £100 and get for ease of maths 100 credits. I used to get low res images for 1 credit but then they all went up to 2 credits. Over night the value of my investment halved.
Recently I had about 48 credits left so could buy 24 low res images. Then iStock changed the structure again so I could only buy a maximum of 10 photos. I am no maths expert but I think that works out that iStock reduced the value of my investment over night by 60%.
My advice do not touch iStock. Overpriced and it wont be long before they change their structure again and you get even less for your money.