In web GUI:
1. Configuratoin->General->Create Image
2. set "type" to "icon"
3. set any name.
4. select png file, which have size 990k-1M
5. save.

After 1-3 minutes system said:

Error in query [insert into images (imageid,name,imagetype,image) values (29,'1',2,'?PNG\r\n\Z\n\0\0\0\rIHDR\0\0\0\01\0\0\0\0??\0\0\0sRGB\0???\0\0\0 pHYs\0\05?\0\05?^e?\0\0\0tIME?38r?e\0\0 \0I

and show all bytes from file.

After that any trying of import images with "type" "background" ends with such error (see above).