You will be well-advised to explore Landsat data, as suggested by Tobias, because they are indeed free of charge and readily accessible, even for the most recent acquisitions. This being said, if you do require SPOT data, it would help to make your request more specific in terms of spatial coverage and timing.
For instance, data from SPOT-4 and 5 that are at least 5 years old are in principle available for free for non-commercial applications:
So, if you mostly require old data (for instance to provide a historical perspective or to study changes over long periods of time), then cost should not be an issue.
Also, there have been plenty of SPOT data actually available for free for specific areas since at least 2010. See this advert for data over the US
http://www.pnamp.org/node/2975
for example. It is only the latest SPOT data from the most advanced sensors (currently 6 and 7) that are for sale (for now). Cheers, Michel.
I can't make commitments for what SPOT is willing to deliver for free worldwide: I only witness what they advertise, and I know what's available here in South Africa, for South Africans. So I suggest you contact either the AIRBUS Defence and Space Headquarters (the current owner of the SPOT series 6 and 7) in France, or their commercial representative in Brazil. You'll find their contacts here (including the office in São Paulo):
That´s my question: Why they have announced about these free historical images if they in fact were not available for the community? I have already lost a lot of time trying to find them.
You can download SPOT-5 satellite images from the USGS Earth Explorer or the USGS Glovis explorer. Though the images do not cover the entire world. It only covers some selected areas.