The problem is you are forgetting the fundamental thing about queries - they return the results in a result identifier and you need to pull the results you want from there. (That's what the Resource message is about.) Also you need to name the column in the result. Here's a bit to get you going:
mysql_result returns one cell or field of a result set.
$counter = mysql_query("SELECT COUNT(*) AS totalresults FROM gallery WHERE Picture_Keywords LIKE \"%$find%\"");
$total = mysql_result($counter,0,0);
mysql_result (resource result, int row [, mixed field])
The first item is the variable you assigned the query to, the second is the row offset (if any, 0 being the first row) from the top of the result set, and the third can be either the column offset (again 0 being the first column) or the name of the column (or in our case the alias we assigned to it - totalresults).