You can search annotation comments and specify only image annotations using the Annotation search type + some advanced search syntax:

An annotation type of "bitmap" corresponds to image annotations. The comment search is an indexed search, so you shouldn't need to use wildcards.

You can also combine the two terms like so:

{LF:anncomment~="your text", LF:Anntype="bitmap"}

Important version notes:

• Support for bitmap annotation type was added in LF Server 9.2, so if you are on an older version, you will not be able to specify bitmap as an annotation type.
  • LF server 8.0+ does support annotation type for redaction, highlight, and stamp, so you could exclude those annotation types if it would help
• Indexed searches for annotation comments was added in 9.1, so older version would use {LF:anncomment="*your text*"}  (no tilde, added leading and trailing wildcards) for a similar result.