>>>>If you use a general field, this field gets associated with a specific program. If this program isn't installed on a machine, the field won't show as expected, which is what you see. That's one of many reasons why general fields should NOT be used. It sounded like a good idea when they were introduced, but experience has shown that they are a real pain to work with. Cyanide is quicker...
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>>>The problem is that if use a blob field and i import a png file (with transparency) then i have problems to show it with crystal reports )it is shown with black background). I have no problems if i import a bmp file in a general field (
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>>A blob field is NOT a general field, and a general field is NOT a blob field. These field types are technically very different. The most important difference is that a general field is tied to an external application, e.g. Excel or Word, while a blob field are "independent" and are usually used together with an Image control using its PictureVal property.
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>> What field type do you use?
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>I am searching a solution that let me to insert in a report (with Crystal report) a sign stored in a png file.... every solution that works is good for me....

This sounds like a Crystal Report problem. Unfortunately I don't use CR, so I can't provide more help.