Download high res NDVI imagery
I don't know about any European database of ready-made high resolution NDVI, but it's relatively easy to create it from raw Landsat imagery in 30m resolution. Access to the Landsat archive is free of charge (only registration needed) via EarthExplorer web service link. In the Data Sets tab, expand "Landsat Archive" list and check L8 checkboxes for contemporary imagery or L4-5 TM for historical imagery. After downloading, you can calculate NDVI using any software with raster calculator capabilities. A lightweight and relatively easy to use example is MultiSpec - website and NDVI tutorial. Pay attention to band numbers - use 5 as NIR and 4 as Red in Landsat 8, or 4 as NIR and 3 as Red in older Landsat (4,5,7).
Free method :
The High-resolution images are not available for free unless you are part of a body of research and teaching. You have two options:
- Free access to the results of NDVI already calculated. For example : http://neo.sci.gsfc.nasa.gov/view.php?datasetId=MOD13A2_E_NDVI&date=2014-06-01
Pay method :
If you can afford you can buy high resolutions pictures like SPOT images at http://www.astrium-geo.com/