Character limitation for String fields?

Summary

Is there a limitation on the length of a string field?

Content

I wanted to store images in a business object, so I thought I would store them as base64 encoded in a String field.  Seems like String fields have a limitation of around 4000 characters.  Is that the case?

Only reason I am trying it this way is because I don't see an option for a Blob field in the business object.