DeepRoot ~ General purpose plant database
This is an excellent, reasonably priced, standalone and web plant database. DeepRoot features mostly European species, but with some useful additions from Australia and New Zealand.
Use DeepRoot to search though > 11,000 records to find just the plant you want.
DeepRoot users have access to a great collection of images that can be used to illustrate your own landscape design ideas. Use DeepRoot images in your plans so they are free from copyright issues. Populate SppDb with DeepRoot images and combine with CAD software such as GardenCAD and gCADPlus.
The figure below shows a high resolution image from DeepRoot added to a SppDb plant list.
DeepRoot also has a free web plant database suitable for casual searching. The result of a search for the annual species - Zinnia is shown below.
Although it is possible to download the image and use it to populate databases such as SppDb, doing just that infringes DeepRoot's copyright. Much better to spend the money on DeeRroot, get higher quality images and free yourself from copyright issues.